net: Fix build when CONFIG_INET is not enabled

If the kernel is configured with CONFIG_NET, but without CONFIG_INET we
get the following error when building:

sock.c:(.text+0x4c17): undefined reference to `__sk_defer_free_flush'

Lets move __sk_defer_free_flush to sock.c

Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>

net/core/sock.c

@@ -2058,6 +2058,20 @@ static void __sk_destruct(struct rcu_head *head)
 	sk_prot_free(sk->sk_prot_creator, sk);
 }
 
+void __sk_defer_free_flush(struct sock *sk)
+{
+	struct llist_node *head;
+	struct sk_buff *skb, *n;
+
+	head = llist_del_all(&sk->defer_list);
+	llist_for_each_entry_safe(skb, n, head, ll_node) {
+		prefetch(n);
+		skb_mark_not_on_list(skb);
+		__kfree_skb(skb);
+	}
+}
+EXPORT_SYMBOL(__sk_defer_free_flush);
+
 void sk_destruct(struct sock *sk)
 {
 	bool use_call_rcu = sock_flag(sk, SOCK_RCU_FREE);

net/ipv4/tcp.c

@@ -1588,20 +1588,6 @@ void tcp_cleanup_rbuf(struct sock *sk, int copied)
 		tcp_send_ack(sk);
 }
 
-void __sk_defer_free_flush(struct sock *sk)
-{
-	struct llist_node *head;
-	struct sk_buff *skb, *n;
-
-	head = llist_del_all(&sk->defer_list);
-	llist_for_each_entry_safe(skb, n, head, ll_node) {
-		prefetch(n);
-		skb_mark_not_on_list(skb);
-		__kfree_skb(skb);
-	}
-}
-EXPORT_SYMBOL(__sk_defer_free_flush);
-
 static void tcp_eat_recv_skb(struct sock *sk, struct sk_buff *skb)
 {
 	__skb_unlink(skb, &sk->sk_receive_queue);