ethoc: enable interrupts after napi_complete

Occasionally, it seems that some race is causing the interrupts to not be
reenabled otherwise with the end result that networking just stops working.
Enabling interrupts after calling napi_complete is more in line with what
other drivers do.

Signed-off-by: Jonas Bonn <jonas@southpole.se>
Signed-off-by: David S. Miller <davem@davemloft.net>