ICMPv6: Send router advertisement from own link-local address

I'm not quite sure how I ended up doing this, but for some strange
reason the code before this commit is sending the ICMPv6 Router
Advertisements from some weird non-standard source address.  This is
a violation of RFC4861 which clearly states that the source address
of router advertisements "MUST be the link-local address assigned to the
interface from which this message is sent."

Change-Id: Ib444af70fc8f0b433d371281601fd5a37b29039e
diff --git a/ggsn/icmpv6.c b/ggsn/icmpv6.c
index ac51bb1..11ced24 100644
--- a/ggsn/icmpv6.c
+++ b/ggsn/icmpv6.c
@@ -179,13 +179,9 @@
 	return true;
 }
 
-/* RFC3307 link-local scope multicast address */
-static const struct in6_addr my_local_addr = {
-	.s6_addr = { 0x01,0x02,0,0,  0,0,0,0, 0,0,0,0,  0,0,0,0xff }
-};
-
 /* handle incoming packets to the all-routers multicast address */
-int handle_router_mcast(struct gsn_t *gsn, struct pdp_t *pdp, const uint8_t *pack, unsigned len)
+int handle_router_mcast(struct gsn_t *gsn, struct pdp_t *pdp, const struct in6_addr *own_ll_addr,
+			const uint8_t *pack, unsigned len)
 {
 	struct ippoolm_t *member = pdp->peer;
 	const struct ip6_hdr *ip6h = (struct ip6_hdr *)pack;
@@ -222,10 +218,10 @@
 				osmo_hexdump(pack, len));
 			return -1;
 		}
-		/* FIXME: Send router advertisement from GGSN link-local
+		/* Send router advertisement from GGSN link-local
 		 * address to MS link-local address, including prefix
 		 * allocated to this PDP context */
-		msg = icmpv6_construct_ra(&my_local_addr, &ip6h->ip6_src, &member->addr.v6);
+		msg = icmpv6_construct_ra(own_ll_addr, &ip6h->ip6_src, &member->addr.v6);
 		/* Send the constructed RA to the MS */
 		gtp_data_req(gsn, pdp, msgb_data(msg), msgb_length(msg));
 		msgb_free(msg);