RX buffer allocation failure is not an input error. Controller

successfully received a frame but we failed to pass it to upper
stack due to lack of resources. So update if_iqdrops counter
instead of updating if_ierrors counter.

sys/dev/usb/net/usb_ethernet.c

@@ -558,7 +558,7 @@ uether_rxbuf(struct usb_ether *ue, struct usb_page_cache *pc,
 
 	m = uether_newbuf();
 	if (m == NULL) {
-		ifp->if_ierrors++;
+		ifp->if_iqdrops++;
 		return (ENOMEM);
 	}