Use active master key in update_princ_encryption

kdb5_util update_princ_encryption should update to the active master
key version, not the most recent.

(cherry picked from commit 4ccc18bc3ddc49d0fd0d2de00ec91c0fa44c53a8)

https://github.com/krb5/krb5/commit/fa728fc6cc8a3379d10cae7876be32d379fc51be
Author: Greg Hudson <ghudson@mit.edu>
Committer: Tom Yu <tlyu@mit.edu>
Commit: fa728fc6cc8a3379d10cae7876be32d379fc51be
Branch: krb5-1.12
 doc/admin/admin_commands/kdb5_util.rst |    4 ++--
 src/kadmin/dbutil/kdb5_mkey.c          |   15 +++++----------
 2 files changed, 7 insertions(+), 12 deletions(-)