myri10ge: get rid of custom busy poll code

Compared to custom busy_poll, the generic NAPI one is simpler and
removes a lot of code. It removes one atomic in the fast path (when
busy poll is not in action) since we do not have to use an extra
spinlock.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>