For TCP streams we used to have three states, e.g. `InitStream`,
`ListenStream`, `ConnectedStream`. If the socket is not bound, it is in
the `InitStream` state. If the socket is bound, it is still in that
state. Most seriously, if the socket is connecting to the remote peer,
but the connection has not been established, it is also in the
`InitStream` state.
While the socket is trying to connect to its peer, it needs to handle
iface events to update its internal state. So it is expected to
implement the trait that observes such events for this later. However,
the reality that sockets connecting to their peers are mixed in with
other unbound and bound sockets in the `InitStream` will complicate
things.
In fact, the connecting socket should belong to an independent state. It
does not share too much logic with unbound and bound sockets in the
`InitStream`. So in this commit we will decouple that and create a new
`ConnectingStream` state.
6b903d0c10