netvsc: Fix a bug in sub-channel handling

All netvsc channels are handled via NAPI. Setup the "read mode" correctly
for the netvsc sub-channels.
Signed-off-by: NK. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/hyperv/rndis_filter.c

@@ -1002,6 +1002,11 @@ static void netvsc_sc_open(struct vmbus_channel *new_sc)
 	if (!nvchan->mrc.buf)
 		return;
 
+	/* Because the device uses NAPI, all the interrupt batching and
+	 * control is done via Net softirq, not the channel handling
+	 */
+	set_channel_read_mode(new_sc, HV_CALL_ISR);
+
 	ret = vmbus_open(new_sc, nvscdev->ring_size * PAGE_SIZE,
 			 nvscdev->ring_size * PAGE_SIZE, NULL, 0,
 			 netvsc_channel_cb, nvchan);