libceph: bump CephXAuthenticate encoding version

A dummy v3 encoding (exactly the same as v2) was introduced so that
the monitors can distinguish broken clients that may not include their
auth ticket in CEPHX_GET_AUTH_SESSION_KEY request on reconnects, thus
failing to prove previous possession of their global_id (one part of
CVE-2021-20288).

The kernel client has always included its auth ticket, so it is
compatible with enforcing mode as is.  However we want to bump the
encoding version to avoid having to authenticate twice on the initial
connect -- all legacy (CephXAuthenticate < v3) are now forced do so in
order to expose insecure global_id reclaim.

Marking for stable since at least for 5.11 and 5.12 it is trivial
(v2 -> v3).

Cc: stable@vger.kernel.org # 5.11+
URL: https://tracker.ceph.com/issues/50452
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Sage Weil <sage@redhat.com>