tc: u32: Fix icmp_code off.

The off of icmp_code is not 20 but 21. Also offmask should be 0 unless
nexthdr+ is specified.
Signed-off-by: Hiroaki SHIMODA <shimoda.hiroaki@gmail.com>

tc/f_u32.c

@@ -531,7 +531,7 @@ static int parse_ip(int *argc_p, char ***argv_p, struct tc_u32_sel *sel)
 		res = parse_u8(&argc, &argv, sel, 20, 0);
 	} else if (strcmp(*argv, "icmp_code") == 0) {
 		NEXT_ARG();
-		res = parse_u8(&argc, &argv, sel, 20, 1);
+		res = parse_u8(&argc, &argv, sel, 21, 0);
 	} else
 		return -1;