net: l2tp_eth: provide tx_dropped counter

Change l2tp_xmit_skb() to return NET_XMIT_DROP in case skb is dropped.

Use kfree_skb() instead dev_kfree_skb() for drop_monitor pleasure.

Support tx_dropped counter for l2tp_eth

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: James Chapman <jchapman@katalix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 32b2155..393355d 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1128,6 +1128,7 @@
 	int headroom;
 	int uhlen = (tunnel->encap == L2TP_ENCAPTYPE_UDP) ? sizeof(struct udphdr) : 0;
 	int udp_len;
+	int ret = NET_XMIT_SUCCESS;
 
 	/* Check that there's enough headroom in the skb to insert IP,
 	 * UDP and L2TP headers. If not enough, expand it to
@@ -1137,8 +1138,8 @@
 		uhlen + hdr_len;
 	old_headroom = skb_headroom(skb);
 	if (skb_cow_head(skb, headroom)) {
-		dev_kfree_skb(skb);
-		goto abort;
+		kfree_skb(skb);
+		return NET_XMIT_DROP;
 	}
 
 	new_headroom = skb_headroom(skb);
@@ -1156,7 +1157,8 @@
 
 	bh_lock_sock(sk);
 	if (sock_owned_by_user(sk)) {
-		dev_kfree_skb(skb);
+		kfree_skb(skb);
+		ret = NET_XMIT_DROP;
 		goto out_unlock;
 	}
 
@@ -1215,8 +1217,7 @@
 out_unlock:
 	bh_unlock_sock(sk);
 
-abort:
-	return 0;
+	return ret;
 }
 EXPORT_SYMBOL_GPL(l2tp_xmit_skb);