be2net: get rid of custom busy poll code

Compared to custom busy_poll, the generic NAPI one is better, since
it allows to use GRO, and it removes a lot of code and extra locked
operations in fast path.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Sathya Perla <sathya.perla@broadcom.com>
Cc: Ajit Khaparde <ajit.khaparde@broadcom.com>
Cc: Sriharsha Basavapatna <sriharsha.basavapatna@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>