rdma: glusterfsd SEGV at volume start

glusterfsd NULL ptr deref in proto/server: get_frame_from_request()
with 'transport rdma' volume

no test case, our regression test framework doesn't have Infiniband.
If it did, the test case would be to create a 'transport rdma' volume,
start it, and create/write/read/delete files on the volume.

Change-Id: I91a6956bdf8f61f3853e0c0951744460ba138576
BUG: 1129708
Signed-off-by: Kaleb S. KEITHLEY <kkeithle@redhat.com>
Reviewed-on: http://review.gluster.org/8479
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>