net/smc: move link group list to smc_core

This patch moves the global link group list to smc_core where the link
group functions are. To make this work, it moves code in af_smc and
smc_ib that operates on the link group list to smc_core as well.

While at it, the link group counter is integrated into the list
structure and initialized to zero.

Signed-off-by: Hans Wippel <hwippel@linux.ibm.com>
Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>