net: ena: make ena rxfh support ETH_RSS_HASH_NO_CHANGE

As the name suggests ETH_RSS_HASH_NO_CHANGE is received upon changing
the key or indirection table using ethtool while keeping the same hash
function.

Also add a function for retrieving the current hash function from
the ena-com layer.

Fixes: 1738cd3e

 ("net: ena: Add a driver for Amazon Elastic Network Adapters (ENA)")
Signed-off-by: Sameeh Jubran <sameehj@amazon.com>
Signed-off-by: Saeed Bshara <saeedb@amazon.com>
Signed-off-by: Arthur Kiyanovski <akiyano@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>