libceph: use the right footer size when skipping a message

libceph: use the right footer size when skipping a message

Orabug: 23330969

[ Upstream commit dbc0d3caff5b7591e0cf8e34ca686ca6f4479ee1 ]

ceph_msg_footer is 21 bytes long, while ceph_msg_footer_old is only 13.
Don't skip too much when CEPH_FEATURE_MSG_AUTH isn't negotiated.

Cc: stable@vger.kernel.org # 3.19+
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Alex Elder <elder@linaro.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
(cherry picked from commit 66333f910d64623fa9cc886c259d57e6d24863cd)

Signed-off-by: Dan Duval <dan.duval@oracle.com>