net/smc: common release code for non-accepted sockets

There are common steps when releasing an accepted or unaccepted socket.
Move this code into a common routine.

Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>