inet: fill request sock ir_iif for IPv4

Once request socks will be in ehash table, they will need to have
a valid ir_iff field.

This is currently true only for IPv6. This patch extends support
for IPv4 as well.

This means inet_diag_fill_req() can now properly use ir_iif,
which is better for IPv6 link locals anyway, as request sockets
and established sockets will propagate consistent netlink idiag_if.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
index 8f6f400..7f6456a 100644
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -643,6 +643,7 @@
 	ireq->ir_rmt_addr = ip_hdr(skb)->saddr;
 	write_pnet(&ireq->ireq_net, sock_net(sk));
 	ireq->ireq_family = AF_INET;
+	ireq->ir_iif = sk->sk_bound_dev_if;
 
 	/*
 	 * Step 3: Process LISTEN state