ntpd: prefer %z when formatting size_t

[Brent Cook]

Pretty trivial conversion. ok?

Index: ntp_msg.c
===================================================================
RCS file: /cvs/src/usr.sbin/ntpd/ntp_msg.c,v
retrieving revision 1.20
diff -u -p -u -p -r1.20 ntp_msg.c
--- ntp_msg.c   9 Jan 2015 07:35:37 -0000       1.20
+++ ntp_msg.c   10 Feb 2015 04:23:03 -0000
@@ -62,7 +62,7 @@ ntp_sendmsg(int fd, struct sockaddr *sa,
        }

        if (n != sizeof(*msg)) {
-               log_warnx("ntp_sendmsg: only %ld of %ld bytes sent", n,
+               log_warnx("ntp_sendmsg: only %zd of %zd bytes sent", n,
                    sizeof(*msg));
                return (-1);
        }