cxgb4: add support to fetch ethtool n-tuple filters

Add support to fetch the requested ethtool n-tuple filters by
translating them from hardware spec to ethtool n-tuple spec.

Signed-off-by: Rahul Lakkireddy <rahul.lakkireddy@chelsio.com>
Signed-off-by: Vishal Kulkarni <vishal@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>