Introduce default rx mode for device drivers

If interface is down and queues are not configured then we are not able
to change rx-mode. This change introducess default mode which is stored
per interface and applied if driver wants.

Change-Id: I70149c21c1530eafc148d5e4aa03fbee53dec62f
Signed-off-by: Damjan Marion <damarion@cisco.com>
diff --git a/src/vnet/interface.c b/src/vnet/interface.c
index e9042ae..1370d04 100644
--- a/src/vnet/interface.c
+++ b/src/vnet/interface.c
@@ -706,6 +706,7 @@
 
   hw_index = hw - im->hw_interfaces;
   hw->hw_if_index = hw_index;
+  hw->default_rx_mode = VNET_HW_INTERFACE_RX_MODE_POLLING;
 
   if (dev_class->format_device_name)
     hw->name = format (0, "%U", dev_class->format_device_name, dev_instance);