net/smc: refactoring initialization of smc sock

This patch aims to isolate the shared components of SMC socket
allocation by introducing smc_sk_init() for sock initialization
and __smc_create_clcsk() for the initialization of clcsock.

This is in preparation for the subsequent implementation of the
AF_INET version of SMC.

Signed-off-by: D. Wythe <alibuda@linux.alibaba.com>
Reviewed-by: Tony Lu <tonylu@linux.alibaba.com>
Reviewed-by: Wenjia Zhang <wenjia@linux.ibm.com>
Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
Tested-by: Niklas Schnelle <schnelle@linux.ibm.com>
Tested-by: Wenjia Zhang <wenjia@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>