client: pass xflags for unlink

Nobody seems to use these currently, but I tried to for some debugging,
and that led to a few head-scratches before I figured out that it wasn't
being passed across the server/client boundary.  Might as well fix it
before somebody tries to use it for real and has to go through the same
exercise.

Change-Id: Ieddfac106103db02fdf488c86f3f979d29a6ab83
BUG: 1158614
Signed-off-by: Jeff Darcy <jdarcy@redhat.com>
Reviewed-on: http://review.gluster.org/8287
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Niels de Vos <ndevos@redhat.com>
Reviewed-by: Pranith Kumar Karampuri <pkarampu@redhat.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>