net: ipv6: more places need LOOPBACK_IFINDEX for flowi6_iif

To properly match iif in ip rules we have to provide
LOOPBACK_IFINDEX in flowi6_iif, not 0. Some ip6mr_fib_lookup
and fib6_rule_lookup callers need such fix.

Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index 8659067..8250474 100644
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -1633,7 +1633,7 @@
 {
 	struct mr6_table *mrt;
 	struct flowi6 fl6 = {
-		.flowi6_iif	= skb->skb_iif,
+		.flowi6_iif	= skb->skb_iif ? : LOOPBACK_IFINDEX,
 		.flowi6_oif	= skb->dev->ifindex,
 		.flowi6_mark	= skb->mark,
 	};