netdev: change transmit to limited range type

The transmit function should only return one of three possible values,
some drivers got confused and returned errno's or other values.
This changes the definition so that this can be caught at compile time.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
1 file changed