OSPF: Packets on PtP networks should be always sent to AllSPFRouters

As specified in RFC 2328 8.1: "On physical point-to-point networks,
the IP destination is always set to the address AllSPFRouters."

Note that this likely break setups with multiple neighbors on a network
configured as PtP, which worked before. These should be configured as
PtMP.

Thanks to Senthil Kumar Nagappan for the original patch and to Joakim
Tjernlund for suggestions.

proto/ospf/lsreq.c

@@ -89,7 +89,7 @@ ospf_send_lsreq(struct ospf_proto *p, struct ospf_neighbor *n)
   pkt->length = htons(length);
 
   OSPF_PACKET(ospf_dump_lsreq, pkt, "LSREQ packet sent to nbr %R on %s", n->rid, ifa->ifname);
-  ospf_send_to(ifa, n->ip);
+  ospf_send_to_nbr(ifa, n);
 }