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.

https://github.com/krb5/krb5/commit/4ccc18bc3ddc49d0fd0d2de00ec91c0fa44c53a8
Author: Greg Hudson <ghudson@mit.edu>
Commit: 4ccc18bc3ddc49d0fd0d2de00ec91c0fa44c53a8
Branch: master
 doc/admin/admin_commands/kdb5_util.rst |    4 ++--
 src/kadmin/dbutil/kdb5_mkey.c          |   15 +++++----------
 2 files changed, 7 insertions(+), 12 deletions(-)