rpc-transport: fix glusterd crash when rdma.so missing

Add checks before trying to delete vol_opt from list and free

Change-Id: I2858f58518394beb8f74fa477be81d7bdd38304f
BUG: 924215
Signed-off-by: Rajesh Amaravathi <rajesh@redhat.com>
Reviewed-on: http://review.gluster.org/4704
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>