net/smc: improve server ISM device determination

Move check whether peer can be reached into smc_pnet_find_ism_by_pnetid().
Thus searching continues for another ism device, if check fails.

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>