inet: constify ip_route_output_flow() socket argument

Very soon, TCP stack might call inet_csk_route_req(), which
calls inet_csk_route_req() with an unlocked listener socket,
so we need to make sure ip_route_output_flow() is not trying to
change any field from its socket argument.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/dst.h b/include/net/dst.h
index df0481a..779206c 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -489,7 +489,8 @@
 #ifndef CONFIG_XFRM
 static inline struct dst_entry *xfrm_lookup(struct net *net,
 					    struct dst_entry *dst_orig,
-					    const struct flowi *fl, struct sock *sk,
+					    const struct flowi *fl,
+					    const struct sock *sk,
 					    int flags)
 {
 	return dst_orig;
@@ -498,7 +499,7 @@
 static inline struct dst_entry *xfrm_lookup_route(struct net *net,
 						  struct dst_entry *dst_orig,
 						  const struct flowi *fl,
-						  struct sock *sk,
+						  const struct sock *sk,
 						  int flags)
 {
 	return dst_orig;
@@ -511,11 +512,11 @@
 
 #else
 struct dst_entry *xfrm_lookup(struct net *net, struct dst_entry *dst_orig,
-			      const struct flowi *fl, struct sock *sk,
+			      const struct flowi *fl, const struct sock *sk,
 			      int flags);
 
 struct dst_entry *xfrm_lookup_route(struct net *net, struct dst_entry *dst_orig,
-				    const struct flowi *fl, struct sock *sk,
+				    const struct flowi *fl, const struct sock *sk,
 				    int flags);
 
 /* skb attached with this dst needs transformation if dst->xfrm is valid */