gve: Handle alternate miss completions

The virtual NIC has 2 ways of indicating a miss-path
completion. This handles the alternate.

Signed-off-by: Jeroen de Borst <jeroendb@google.com>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>