netvsc: don't signal host twice if empty

When hv_pkt_iter_next() returns NULL, it has already called
hv_pkt_iter_close(). Calling it twice can lead to extra host signal.
Signed-off-by: NStephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/hyperv/netvsc.c

@@ -1191,10 +1191,6 @@ int netvsc_poll(struct napi_struct *napi, int budget)
 		nvchan->desc = hv_pkt_iter_next(channel, nvchan->desc);
 	}
 
-	/* if ring is empty, signal host */
-	if (!nvchan->desc)
-		hv_pkt_iter_close(channel);
-
 	/* If send of pending receive completions suceeded
 	 *   and did not exhaust NAPI budget this time
 	 *   and not doing busy poll