Increment queue drops in the network statistics when transmitted packets

are dropped by the mlx4en(4) driver.

Submitted by:		Sepherosa Ziehau <sephe@dragonflybsd.org>
MFC after:		3 days
Sponsored by:		Mellanox Technologies

sys/dev/mlx4/mlx4_en/mlx4_en_tx.c

@@ -1071,6 +1071,10 @@ mlx4_en_transmit(struct ifnet *dev, struct mbuf *m)
 		taskqueue_enqueue(cq->tq, &cq->cq_task);
 	}
 
+#if __FreeBSD_version >= 1100000
+	if (unlikely(err != 0))
+		if_inc_counter(dev, IFCOUNTER_IQDROPS, 1);
+#endif
 	return (err);
 }