glusterd: Update comment with op-version mapping

Change-Id: If024921f2ce2c2d7c94b4a490585130dcf108d53
BUG: 981278
Signed-off-by: Kaushal M <kaushal@redhat.com>
Reviewed-on: http://review.gluster.org/5288
Reviewed-by: Vijay Bellur <vbellur@redhat.com>
Tested-by: Vijay Bellur <vbellur@redhat.com>