net/smc: retrieve v2 gid from IB device

In smc_ib.c, scan for RoCE devices that support UDP encapsulation.
Find an eligible device and check that there is a route to the
remote peer.

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