traceroute: fix compile error due to FreeBSD compat

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

networking/traceroute.c

@@ -713,11 +713,16 @@ packet4_ok(int read_len, int seq)
 			up = (struct udphdr *)((char *)hip + hlen);
 			if (hlen + 12 <= read_len
 			 && hip->ip_p == IPPROTO_UDP
-// Off: since we do not form the entire IP packet,
+#if !defined(__FreeBSD__)
+// Disabled source check: since we do not form the entire IP packet,
 // but defer it to kernel, we can't set source port,
 // and thus can't check it here in the reply
+			/* && up->source == ident */
+			 && up->dest == htons(port + seq)
+#else
 			/* && up->uh_sport == ident */
 			 && up->uh_dport == htons(port + seq)
+#endif
 			) {
 				return (type == ICMP_TIMXCEED ? -1 : code + 1);
 			}