cxgb4: remove stats fetched from firmware

When running ethtool -S, some stats are requested from firmware.
Since getting these stats via firmware mailbox is slow, some packets
get dropped under heavy load while running ethtool -S.

So, remove these stats from ethtool -S.

Signed-off-by: Rahul Lakkireddy <rahul.lakkireddy@chelsio.com>
Signed-off-by: Ganesh Goudar <ganeshgr@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>