ipv4: Optimize flow initialization in fib_validate_source().

Like in commit 44713b67
("ipv4: Optimize flow initialization in output route lookup."
we can optimize the on-stack flow setup to only initialize
the members which are actually used.

Otherwise we bzero the entire structure, then initialize
explicitly the first half of it.
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/fib_frontend.c

@@ -193,19 +193,21 @@ int fib_validate_source(__be32 src, __be32 dst, u8 tos, int oif,
 			u32 *itag, u32 mark)
 {
 	struct in_device *in_dev;
-	struct flowi fl = {
-		.fl4_dst = src,
-		.fl4_src = dst,
-		.fl4_tos = tos,
-		.mark = mark,
-		.iif = oif
-	};
+	struct flowi fl;
 	struct fib_result res;
 	int no_addr, rpf, accept_local;
 	bool dev_match;
 	int ret;
 	struct net *net;
 
+	fl.oif = 0;
+	fl.iif = oif;
+	fl.mark = mark;
+	fl.fl4_dst = src;
+	fl.fl4_src = dst;
+	fl.fl4_tos = tos;
+	fl.fl4_scope = RT_SCOPE_UNIVERSE;
+
 	no_addr = rpf = accept_local = 0;
 	in_dev = __in_dev_get_rcu(dev);
 	if (in_dev) {