ovl: remove posix_acl_default from workdir

[ Upstream commit c11b9fdd6a612f376a5e886505f1c54c16d8c380 ]

Clear out posix acl xattrs on workdir and also reset the mode after
creation so that an inherited sgid bit is cleared.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>