ipv4: Loosen source address check on IPv4 output

ip_route_output() contains a check to make sure that no flows with
non-local source IP addresses are routed. This obviously makes using
such addresses impossible.

This patch introduces a flowi flag which makes omitting this check
possible. The new flag provides a way of handling transparent and
non-transparent connections differently.

Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: KOVACS Krisztian <hidden@sch.bme.hu>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/flow.h b/include/net/flow.h
index 228b247..b45a5e4 100644
--- a/include/net/flow.h
+++ b/include/net/flow.h
@@ -47,6 +47,8 @@
 #define fl4_scope	nl_u.ip4_u.scope
 
 	__u8	proto;
+	__u8	flags;
+#define FLOWI_FLAG_ANYSRC 0x01
 	union {
 		struct {
 			__be16	sport;