cxgb4: add ethtool n-tuple filter deletion

Add support to delete ethtool n-tuple filter. Fetch the appropriate
filter region (HPFILTER, HASH, NORMAL) in which the filter exists,
and delete it from the respective region, accordingly.

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>