revert e3c5de1 (#425)

src/if-bsd.c

@@ -741,6 +741,19 @@ if_route(unsigned char cmd, const struct rt *rt)
 		    !sa_is_loopback(&rt->rt_gateway))
 		{
 			rtm->rtm_index = (unsigned short)rt->rt_ifp->index;
+/*
+ * OpenBSD rejects the message for on-link routes.
+ * FreeBSD-12 kernel apparently panics.
+ * I can't replicate the panic, but better safe than sorry!
+ * https://roy.marples.name/archives/dhcpcd-discuss/0002286.html
+ *
+ * Neither OS currently allows IPv6 address sharing anyway, so let's
+ * try to encourage someone to fix that by logging a waring during compile.
+ */
+#if defined(__FreeBSD__) || defined(__OpenBSD__)
+#warning kernel does not allow IPv6 address sharing
+			if (!gateway_unspec || rt->rt_dest.sa_family!=AF_INET6)
+#endif
 			rtm->rtm_addrs |= RTA_IFP;
 			if (!sa_is_unspecified(&rt->rt_ifa))
 				rtm->rtm_addrs |= RTA_IFA;