cluster/dht: mark linkfile creation/deletion as internal fop

Currently dht creates/deletes linkfiles for various ops like
rename/linking and when layout changes. dht_linkfile_create
already sends a key GLUSTERFS_INTERNAL_FOP_KEY in dict to
identify this as an internal fop and not user based op.

Enhancing rename related links/unlinks to send this key too.
Marker/changelog or other xlators can now identify these as
internal fops and handle them accordingly

Change-Id: Ib1ca789e6dbce48703c55ad3f4f88f7cd2df3d06
BUG: 987428
Signed-off-by: shishir gowda <sgowda@redhat.com>
Reviewed-on: http://review.gluster.org/5335
Reviewed-by: Amar Tumballi <amarts@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>