net/smc: introduce CLC first contact extension

SMC Version 2 defines a first contact extension for CLC accept
and CLC confirm. This patch covers sending and receiving of the
CLC first contact extension.

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>