Ensure array count consistency in kadm5 RPC

Ensure array count consistency in kadm5 RPC

In _xdr_kadm5_principal_ent_rec(), ensure that n_key_data matches the
key_data array count when decoding.  Otherwise when the structure is
later freed, xdr_array() could iterate over the wrong number of
elements, either leaking some memory or freeing uninitialized
pointers.  Reported by Robert Morris.

CVE-2023-36054:

An authenticated attacker can cause a kadmind process to crash by
freeing uninitialized pointers.  Remote code execution is unlikely.
An attacker with control of a kadmin server can cause a kadmin client
to crash by freeing uninitialized pointers.

(cherry picked from commit ef08b09c9459551aabbe7924fb176f1583053cdd)

ticket: 9099
version_fixed: 1.20.2