ixgbe: get rid of custom busy polling code

ixgbe: get rid of custom busy polling code

In linux-4.5, busy polling was implemented in core
NAPI stack, meaning that all custom implementation can
be removed from drivers.

Not only we remove lot's of code, we also remove one lock
operation in fast path, and allow GRO to do its job.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Acked-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Orabug: 26242766
(cherry picked from commit 3ffc1af576550ec61d35668485954e49da29d168)
Signed-off-by: Jack Vogel <jack.vogel@oracle.com>
Reviewed-by: Ethan Zhao <ethan.zhao@oracle.com>