tun: Update classid on packet injection

This patch makes tun update its socket classid every time we
inject a packet into the network stack.  This is so that any
updates made by the admin to the process writing packets to
tun is effected.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/sock.c b/net/core/sock.c
index a05ae7f..37fe9b6 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1064,6 +1064,7 @@
 	if (classid && classid != sk->sk_classid)
 		sk->sk_classid = classid;
 }
+EXPORT_SYMBOL(sock_update_classid);
 #endif
 
 /**