Make decryption of master key list more robust

Make decryption of master key list more robust

krb5_def_fetch_mkey_list was incorrectly filtering mkey_aux entries
when searching the list for an entry which can be decrypted with the
stashed master key.  This bug was masked in most cases by the mkvno
heuristic.

Remove the mkvno heuristic, since performance is not an issue for this
rarely-performed operation, and remove the incorrect enctype
comparison in the brute-force search.

ticket: 6652
target_version: 1.8
tags: pullup

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@23677 dc483132-0cff-0310-8789-dd5450dbe970