IB/cm: cm_init_av_by_path should find a GID by its netdevice

Previously, the CM has searched the cache for any sgid_index whose
GID matches the path's GID. Since the path record stores the net
device, the CM should now search only for GIDs which originated from
this net device.

Signed-off-by: Matan Barak <matanb@mellanox.com>
Reviewed-By: Devesh Sharma <devesh.sharma@avagotech.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>