Fix kpropd -x

A missing break in the switch statement caused kpropd -x to error out
with a usage message.

(cherry picked from commit 75b2ec88c4d75e7215322d2f0019307310cc9701)

https://github.com/krb5/krb5/commit/57f106a68ed91d2930faadb7667cdfaa074c07c3
Author: Greg Hudson <ghudson@mit.edu>
Committer: Tom Yu <tlyu@mit.edu>
Commit: 57f106a68ed91d2930faadb7667cdfaa074c07c3
Branch: krb5-1.12
 src/slave/kpropd.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)