net/smc: remove unused constant

Constant SMC_CLOSE_WAIT_LISTEN_CLCSOCK_TIME is defined, but since
commit 3d502067

 ("net/smc: simplify wait when closing listen socket")
no longer used. Remove it.

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>