sfc: Call netif_napi_add() before registering our interrupt handler

If we use a shared legacy IRQ then our interrupt handler may be called
as soon as it is registered even though IRQs are disabled on the NIC.
Now that the legacy interrupt handler also checks for event delivery,
it may decide to schedule polling in this case.  Ensure that the NAPI
context is valid but disabled at this point.
Signed-off-by: NBen Hutchings <bhutchings@solarflare.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/sfc/efx.c

@@ -448,6 +448,9 @@ static void efx_init_channels(struct efx_nic *efx)
 
 		WARN_ON(channel->rx_pkt != NULL);
 		efx_rx_strategy(channel);
+
+		netif_napi_add(channel->napi_dev, &channel->napi_str,
+			       efx_poll, napi_weight);
 	}
 }
 
@@ -462,10 +465,6 @@ static void efx_start_channel(struct efx_channel *channel)
 
 	EFX_LOG(channel->efx, "starting chan %d\n", channel->channel);
 
-	if (!(channel->efx->net_dev->flags & IFF_UP))
-		netif_napi_add(channel->napi_dev, &channel->napi_str,
-			       efx_poll, napi_weight);
-
 	/* The interrupt handler for this channel may set work_pending
 	 * as soon as we enable it.  Make sure it's cleared before
 	 * then.  Similarly, make sure it sees the enabled flag set. */