Currently, rcv_msg() always returns zero on a packet delivery upcall
from net_device.

To make its behavior more compliant with the way this API should be
used, we change this to let it return NET_RX_SUCCESS (which is zero
anyway) when it is able to handle the packet, and NET_RX_DROP otherwise.
The latter does not imply any functional change, it only enables the
driver to keep more accurate statistics about the fate of delivered
packets.
Signed-off-by: NYing Xue <ying.xue@windriver.com>
Reviewed-by: NPaul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: NJon Maloy <jon.maloy@ericsson.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>