Box the large structure `AnyUnboundSocket`

So far it is quite common to put the `AnyUnboundSocket` in an enum
variant, e.g. the following code snippet.
```rust
enum Inner {
    Unbound(AlwaysSome<Box<AnyUnboundSocket>>),
    Bound(AlwaysSome<Arc<AnyBoundSocket>>),
    // ...
}
```

However, this pattern is very memory inefficient because the size
difference between two enum variants is significant. The size of
`AnyUnboundSocket` is much larger than the size of
`Arc<AnyBoundSocket>`, where the latter is simply a pointer and a
reference counter.

In fact, we're about to trigger Clippy's large_enum_variant warning.
We're just below its threshold, so the warning doesn't appear.

The solution is simple: If we put `AnyBoundSocket` in `Arc`, we should
also put `AnyUnboundSocket` in `Box`. This way the sizes of different
enum variants will be similar.

services/libs/jinux-std/src/net/iface/common.rs

@@ -98,9 +98,9 @@ impl IfaceCommon {
     pub(super) fn bind_socket(
         &self,
         iface: Arc<dyn Iface>,
-        socket: AnyUnboundSocket,
+        socket: Box<AnyUnboundSocket>,
         config: BindPortConfig,
-    ) -> core::result::Result<Arc<AnyBoundSocket>, (Error, AnyUnboundSocket)> {
+    ) -> core::result::Result<Arc<AnyBoundSocket>, (Error, Box<AnyUnboundSocket>)> {
         let port = if let Some(port) = config.port() {
             port
         } else {

services/libs/jinux-std/src/net/iface/mod.rs

@@ -37,9 +37,9 @@ pub trait Iface: internal::IfaceInternal + Send + Sync {
     /// See discussion at https://github.com/smoltcp-rs/smoltcp/issues/779.
     fn bind_socket(
         &self,
-        socket: AnyUnboundSocket,
+        socket: Box<AnyUnboundSocket>,
         config: BindPortConfig,
-    ) -> core::result::Result<Arc<AnyBoundSocket>, (Error, AnyUnboundSocket)> {
+    ) -> core::result::Result<Arc<AnyBoundSocket>, (Error, Box<AnyUnboundSocket>)> {
         let common = self.common();
         let socket_type_inner = socket.socket_family();
         common.bind_socket(self.arc_self(), socket, config)

services/libs/jinux-std/src/net/socket/ip/common.rs

@@ -40,10 +40,10 @@ fn get_ephemeral_iface(remote_ip_addr: &IpAddress) -> Arc<dyn Iface> {
 }
 
 pub(super) fn bind_socket(
-    unbound_socket: AnyUnboundSocket,
+    unbound_socket: Box<AnyUnboundSocket>,
     endpoint: IpEndpoint,
     can_reuse: bool,
-) -> core::result::Result<Arc<AnyBoundSocket>, (Error, AnyUnboundSocket)> {
+) -> core::result::Result<Arc<AnyBoundSocket>, (Error, Box<AnyUnboundSocket>)> {
     let iface = match get_iface_to_bind(&endpoint.addr) {
         Some(iface) => iface,
         None => {

services/libs/jinux-std/src/net/socket/ip/datagram.rs

@@ -27,7 +27,7 @@ pub struct DatagramSocket {
 }
 
 enum Inner {
-    Unbound(AlwaysSome<AnyUnboundSocket>),
+    Unbound(AlwaysSome<Box<AnyUnboundSocket>>),
     Bound(Arc<BoundDatagram>),
 }
 
@@ -148,7 +148,7 @@ impl Inner {
 
 impl DatagramSocket {
     pub fn new(nonblocking: bool) -> Self {
-        let udp_socket = AnyUnboundSocket::new_udp();
+        let udp_socket = Box::new(AnyUnboundSocket::new_udp());
         Self {
             inner: RwLock::new(Inner::Unbound(AlwaysSome::new(udp_socket))),
             nonblocking: AtomicBool::new(nonblocking),
@@ -176,16 +176,17 @@ impl DatagramSocket {
     }
 
     fn try_bind_empheral(&self, remote_endpoint: &IpEndpoint) -> Result<Arc<BoundDatagram>> {
+        // Fast path
         if let Inner::Bound(bound) = &*self.inner.read() {
             return Ok(bound.clone());
         }
 
+        // Slow path
         let mut inner = self.inner.write();
         if let Inner::Bound(bound) = &*inner {
-            Ok(bound.clone())
-        } else {
-            inner.bind_to_ephemeral_endpoint(remote_endpoint)
+            return Ok(bound.clone());
         }
+        inner.bind_to_ephemeral_endpoint(remote_endpoint)
     }
 }
 

services/libs/jinux-std/src/net/socket/ip/stream/init.rs

@@ -16,7 +16,7 @@ pub struct InitStream {
 }
 
 enum Inner {
-    Unbound(AlwaysSome<AnyUnboundSocket>),
+    Unbound(AlwaysSome<Box<AnyUnboundSocket>>),
     Bound(AlwaysSome<Arc<AnyBoundSocket>>),
     Connecting {
         bound_socket: Arc<AnyBoundSocket>,
@@ -114,7 +114,7 @@ impl Inner {
 
 impl InitStream {
     pub fn new(nonblocking: bool) -> Self {
-        let socket = AnyUnboundSocket::new_tcp();
+        let socket = Box::new(AnyUnboundSocket::new_tcp());
         let inner = Inner::Unbound(AlwaysSome::new(socket));
         Self {
             is_nonblocking: AtomicBool::new(nonblocking),

services/libs/jinux-std/src/net/socket/ip/stream/listen.rs

@@ -133,7 +133,7 @@ impl BacklogSocket {
             Errno::EINVAL,
             "the socket is not bound",
         ))?;
-        let unbound_socket = AnyUnboundSocket::new_tcp();
+        let unbound_socket = Box::new(AnyUnboundSocket::new_tcp());
         let bound_socket = {
             let iface = bound_socket.iface();
             let bind_port_config = BindPortConfig::new(local_endpoint.port, true)?;