s390/net: Remove NETIUCV device driver

The netiucv driver creates TCP/IP interfaces over IUCV between Linux
guests on z/VM and other z/VM entities.

Rationale for removal:
- NETIUCV connections are only supported for compatibility with
  earlier versions and not to be used for new network setups,
  since at least Linux kernel 4.0.
- No known active users, use cases, or product dependencies
- The driver is no longer relevant for z/VM networking;
  preferred methods include:
	* Device pass-through (e.g., OSA, RoCE)
	* z/VM Virtual Switch (VSWITCH)

The IUCV mechanism itself remains supported and is actively used
via AF_IUCV, hvc_iucv, and smsg_iucv.

Signed-off-by: Nagamani PV <nagamani@linux.ibm.com>
Reviewed-by: Alexandra Winter <wintera@linux.ibm.com>
Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250715074210.3999296-1-wintera@linux.ibm.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/arch/s390/driver-model.rst

@@ -305,24 +305,3 @@ xpram shows up under devices/system/ as 'xpram'.
 
 For each cpu, a directory is created under devices/system/cpu/. Each cpu has an
 attribute 'online' which can be 0 or 1.
-
-
-4. Other devices
-----------------
-
-4.1 Netiucv
------------
-
-The netiucv driver creates an attribute 'connection' under
-bus/iucv/drivers/netiucv. Piping to this attribute creates a new netiucv
-connection to the specified host.
-
-Netiucv connections show up under devices/iucv/ as "netiucv<ifnum>". The interface
-number is assigned sequentially to the connections defined via the 'connection'
-attribute.
-
-user
-    - shows the connection partner.
-
-buffer
-    - maximum buffer size. Pipe to it to change buffer size.

drivers/s390/net/Kconfig

@@ -17,18 +17,6 @@ config CTCM
 	  To compile into the kernel, choose Y.
 	  If you do not need any channel-to-channel connection, choose N.
 
-config NETIUCV
-	def_tristate m
-	prompt "IUCV network device support (VM only)"
-	depends on IUCV && NETDEVICES
-	help
-	  Select this option if you want to use inter-user communication
-	  vehicle networking under VM or VIF. It enables a fast communication
-	  link between VM guests. Using ifconfig a point-to-point connection
-	  can be established to the Linux on IBM System z
-	  running on the other VM guest. To compile as a module, choose M.
-	  The module name is netiucv. If unsure, choose Y.
-
 config SMSGIUCV
 	def_tristate m
 	prompt "IUCV special message support (VM only)"

drivers/s390/net/Makefile

@@ -5,7 +5,6 @@
 
 ctcm-y += ctcm_main.o ctcm_fsms.o ctcm_mpc.o ctcm_sysfs.o ctcm_dbug.o
 obj-$(CONFIG_CTCM) += ctcm.o fsm.o
-obj-$(CONFIG_NETIUCV) += netiucv.o fsm.o
 obj-$(CONFIG_SMSGIUCV) += smsgiucv.o
 obj-$(CONFIG_SMSGIUCV_EVENT) += smsgiucv_app.o
 qeth-y += qeth_core_sys.o qeth_core_main.o qeth_core_mpc.o qeth_ethtool.o