nfs: Fix for NFS crash during blocking NLM call.

Bug 990887: During a blocking NLM call NFS server is crashing.

Cause: When nlm4_establish_callback function is called from nlm4svc_send_granted the cs->req->trans
pointer is NULL. Thus using this pointer will result in a crash. Whereas cs->trans points to a
valid transport object. NLM should use cs->trans instead of cs->req->trans.

Fix: Replaced cs->req->trans with cs->trans.

Backport of: http://review.gluster.org/#/c/5452/

BUG: 990887
Change-Id: I33d4b6634752333d6791b1a47ebf10c787c22120
Signed-off-by: Justin Clift <justin@gluster.org>
Reviewed-on: http://review.gluster.org/7478
Reviewed-by: Harshavardhana <harsha@harshavardhana.net>
Reviewed-by: Kaleb KEITHLEY <kkeithle@redhat.com>