glusterd: Syncop callbks should take big lock too

Change-Id: I5ae71ab98f9a336dc9bbf0e7b2ec50a6ed42b0f5
BUG: 948686
Signed-off-by: Krishnan Parthasarathi <kparthas@redhat.com>
Reviewed-on: http://review.gluster.org/4938
Reviewed-by: Amar Tumballi <amarts@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>