Interpret 'prefixlen 0' as the maximum prefix length, as ifconfig

has always done.

sbin/ifconfig/util.c

@@ -1,4 +1,4 @@
-/*	$NetBSD: util.c,v 1.2 2008/05/06 16:09:18 dyoung Exp $	*/
+/*	$NetBSD: util.c,v 1.3 2008/05/07 18:17:42 dyoung Exp $	*/
 
 /*-
  * Copyright (c)2008 David Young.  All rights reserved.
@@ -175,6 +175,9 @@ prefixlen_to_mask(int af, int plen)
 		return NULL;
 	}
 
+	if (plen == 0)
+		plen = addrlen * NBBY;
+
 	memset(addr, 0xff, (plen + NBBY - 1) / NBBY);
 
 	nbit = plen % NBBY;