net: export attach/detach filter routines

Export sk_attach_filter/sk_detach_filter routines,
so that tun module can use them.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/filter.c b/net/core/filter.c
index 08db7b9..7517110 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -529,6 +529,7 @@
 		sk_filter_delayed_uncharge(sk, old_fp);
 	return 0;
 }
+EXPORT_SYMBOL_GPL(sk_attach_filter);
 
 int sk_detach_filter(struct sock *sk)
 {
@@ -545,3 +546,4 @@
 	rcu_read_unlock_bh();
 	return ret;
 }
+EXPORT_SYMBOL_GPL(sk_detach_filter);