Add syntax for rule prio help text.

From: Alexander Wirt <formorer@debian.org>

Add [ prio NUMBER ] to ip_rule.c

See Debian bug #213673 - http://bugs.debian.org/213673

diff -urNad iproute-20070313~/ip/iprule.c iproute-20070313/ip/iprule.c
--- iproute-20070313~/ip/iprule.c	2007-03-13 22:50:56.000000000 +0100
+++ iproute-20070313/ip/iprule.c	2007-06-10 17:54:46.000000000 +0200
@@ -38,7 +38,7 @@
 {
 	fprintf(stderr, "Usage: ip rule [ list | add | del | flush ] SELECTOR ACTION\n");
 	fprintf(stderr, "SELECTOR := [ not ] [ from PREFIX ] [ to PREFIX ] [ tos TOS ] [ fwmark FWMARK[/MASK] ]\n");
-	fprintf(stderr, "            [ dev STRING ] [ pref NUMBER ]\n");
+	fprintf(stderr, "            [ dev STRING ] [ pref NUMBER ] [ prio NUMBER ]\n");
 	fprintf(stderr, "ACTION := [ table TABLE_ID ]\n");
 	fprintf(stderr, "          [ prohibit | reject | unreachable ]\n");
 	fprintf(stderr, "          [ realms [SRCREALM/]DSTREALM ]\n");