Add key/type pair to volume_options.

This avoids warning message to be logged for internal option
 `transport.socket.lowlat' as not being recognized, when transport/ib-verbs is
 used.

Signed-off-by: Sachidananda Urs <sac@gluster.com>
Signed-off-by: Anand V. Avati <avati@dev.gluster.com>

BUG: 818 (transport.socket.lowlat option is not given  as can be seen from the vol-file still the warning shows up in the logs)
URL: http://bugs.gluster.com/cgi-bin/bugzilla3/show_bug.cgi?id=818

xlators/protocol/transport/ib-verbs/src/ib-verbs.c

@@ -2609,5 +2609,8 @@ struct volume_options options[] = {
                     "unix", "inet-sdp" },
           .type  = GF_OPTION_TYPE_STR 
         },
+        { .key   = {"transport.socket.lowlat"},
+          .type  = GF_OPTION_TYPE_BOOL
+        },
         { .key = {NULL} }
 };