xfs: rw remount with unknown ro-compat features

xfs: rw remount with unknown ro-compat features

Although ro-compat features cannot be mounted rw, a bug allows an
ro->rw remount transition, and this will corrupt the filesystem if
it contains ro-compat features unknown to the running kernel.

This bug has been fixed on linux kernel (d0a58e8 xfs: disallow rw
remount on fs with unknown ro-compat features), this case is the
regression testcase of that bug.

Signed-off-by: Zorro Lang <zlang@redhat.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>