Hide the user/password combination in smtpd's logs.

Reference: /n/sources/patch/applied/smtpd-hide-pass
Date: Fri Nov 19 20:52:40 CET 2004

--- /sys/src/cmd/upas/smtp/smtpd.c	Fri Nov 19 20:52:41 2004
+++ /sys/src/cmd/upas/smtp/smtpd.c	Fri Nov 19 20:52:40 2004
@@ -1347,7 +1347,7 @@
 		goto bomb_out;
 
  	syslog(0, "smtpd", "auth(%s, %s) from %s", s_to_c(mech),
-		resp==nil?"nil":s_to_c(resp), him);
+		"(protected)", him);
 
 	if (authenticated) {
 	bad_sequence: