ipv4: fix rcu splat

free_nh_exceptions() should use rcu_dereference_protected(..., 1)
since its called after one RCU grace period.

Also add some const-ification in recent code.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 3ea4652..c7a4de0 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -806,8 +806,8 @@
 
 static struct dst_entry *inet_csk_rebuild_route(struct sock *sk, struct flowi *fl)
 {
-	struct inet_sock *inet = inet_sk(sk);
-	struct ip_options_rcu *inet_opt;
+	const struct inet_sock *inet = inet_sk(sk);
+	const struct ip_options_rcu *inet_opt;
 	__be32 daddr = inet->inet_daddr;
 	struct flowi4 *fl4;
 	struct rtable *rt;