ipv6: Implement IPV6_UNICAST_IF socket option.

The IPV6_UNICAST_IF feature is the IPv6 compliment to IP_UNICAST_IF.

Signed-off-by: Erich E. Hoover <ehoover@mines.edu>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c
index d02f7e4..5bddea7 100644
--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c
@@ -856,6 +856,8 @@
 
 	if (!fl6.flowi6_oif && ipv6_addr_is_multicast(&fl6.daddr))
 		fl6.flowi6_oif = np->mcast_oif;
+	else if (!fl6.flowi6_oif)
+		fl6.flowi6_oif = np->ucast_oif;
 	security_sk_classify_flow(sk, flowi6_to_flowi(&fl6));
 
 	dst = ip6_dst_lookup_flow(sk, &fl6, final_p, true);