LU-7508 ldlm: Don't check opcode with NULL rq_reqmsg

LU-7508 ldlm: Don't check opcode with NULL rq_reqmsg

When GSS is enabled it's possible to have a NULL rq_reqmsg
if a bad signature or no context is returned during the unwrap
of the request.  Don't check the opcode in this case.

Signed-off-by: Jeremy Filizetti <jeremy.filizetti@gmail.com>
Change-Id: I3a74dff7638b318190c5c4ad73acbe7ec299aa80
Reviewed-on: http://review.whamcloud.com/17414
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>