Fix decoding of mkey kvno in mkey_aux tl-data

Fix decoding of mkey kvno in mkey_aux tl-data

krb5_dbe_lookup_mkey_aux was decoding a 16-bit value directly into an
int, resulting in the wrong value on big-endian platforms.  The
consequences are mostly invisible because we ignore this field and try
all mkey_aux nodes in krb5_def_fetch_mkey_list.

(cherry picked from commit 64ec2941af1561ef06e7e885b2ffb65a675516ce)

ticket: 7746 (new)
version_fixed: 1.11.4
status: resolved