tc: pedit: Fix retain value for ihl adjustments

Since the IP Header Length field is just half a byte, adjust retain to
only match these bits so the Version field is not overwritten by
accident.

The whole concept is actually broken due to dependency on endianness
which pedit ignores.
Signed-off-by: Phil Sutter <phil@nwl.cc>

tc/p_ip.c

@@ -58,7 +58,7 @@ parse_ip(int *argc_p, char ***argv_p,struct tc_pedit_sel *sel,struct tc_pedit_ke
 	if (strcmp(*argv, "ihl") == 0) {
 		NEXT_ARG();
 		tkey->off = 0;
-		res = parse_cmd(&argc, &argv, 1, TU32,RU8,sel,tkey);
+		res = parse_cmd(&argc, &argv, 1, TU32,0x0f,sel,tkey);
 		goto done;
 	}
 	if (strcmp(*argv, "protocol") == 0) {