fuse-bridge: fix some breakages from lock migration patch

- do not attempt lock migration if no locks were ever acquired on
  an fd.

- fix fd_lk_ctx_t ref leak during fd migration

- remove spurious fd_unref() (probably added to compensate for
  the fd_ref leak in syncop_open_cbk)

- remove @newfdptr out-param which makes fd ref management really
  tricky (and currently refs were unmanaged for the out-param).
  Instead acquire ref and unref within lock migration function.

Change-Id: I4cc9c451f0df4c051612bd1fa7bef11e801570e4
BUG: 808400
Signed-off-by: Anand Avati <avati@redhat.com>
Reviewed-on: http://review.gluster.org/4453
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Raghavendra Bhat <raghavendra@redhat.com>