ipv6: constify inet6_csk_route_req() socket argument

socket is not modified, make it const so that callers can
do the same if they need.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/inet6_connection_sock.h

@@ -25,7 +25,7 @@ struct sockaddr;
 int inet6_csk_bind_conflict(const struct sock *sk,
 			    const struct inet_bind_bucket *tb, bool relax);
 
-struct dst_entry *inet6_csk_route_req(struct sock *sk, struct flowi6 *fl6,
+struct dst_entry *inet6_csk_route_req(const struct sock *sk, struct flowi6 *fl6,
 				      const struct request_sock *req);
 
 struct request_sock *inet6_csk_search_req(struct sock *sk,

net/ipv6/inet6_connection_sock.c

@@ -65,7 +65,7 @@ int inet6_csk_bind_conflict(const struct sock *sk,
 }
 EXPORT_SYMBOL_GPL(inet6_csk_bind_conflict);
 
-struct dst_entry *inet6_csk_route_req(struct sock *sk,
+struct dst_entry *inet6_csk_route_req(const struct sock *sk,
 				      struct flowi6 *fl6,
 				      const struct request_sock *req)
 {