vxlan: Add missing VNI filter counter update in arp_reduce().

VXLAN stores per-VNI statistics using vxlan_vnifilter_count().
These statistics were not updated when arp_reduce() failed its
pskb_may_pull() call.

Use vxlan_vnifilter_count() to update the VNI counter when that
happens.

Fixes: 4095e0e ("drivers: vxlan: vnifilter: per vni stats")
Signed-off-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: Guillaume Nault

drivers/net/vxlan/vxlan_core.c

@@ -1838,6 +1838,8 @@ static int arp_reduce(struct net_device *dev, struct sk_buff *skb, __be32 vni)
 
 	if (!pskb_may_pull(skb, arp_hdr_len(dev))) {
 		dev_core_stats_tx_dropped_inc(dev);
+		vxlan_vnifilter_count(vxlan, vni, NULL,
+				      VXLAN_VNI_STATS_TX_DROPS, 0);
 		goto out;
 	}
 	parp = arp_hdr(skb);