cxgb4: implement ethtool dump data operations

Implement operations to set/get dump data via ethtool.  Also add
template header that precedes dump data, which helps in decoding
and extracting the dump data.

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>