cxgb4: add support to retrieve stats for hash filters

Add support to retrieve packet-count and byte-count for hash-filters
by retrieving filter-entry appropriately based on whether the
request is for hash-filter or not.

Signed-off-by: Kumar Sanghvi <kumaras@chelsio.com>
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>