net: ena: avoid unnecessary admin command when RSS function set fails

Currently when ena_set_hash_function() fails the hash function is
restored to the previous value by calling an admin command to get
the hash function from the device.

In this commit we avoid the admin command, by saving the previous
hash function before calling ena_set_hash_function() and using this
previous value to restore the hash function in case of failure of
ena_set_hash_function().

Signed-off-by: Sameeh Jubran <sameehj@amazon.com>
Signed-off-by: Arthur Kiyanovski <akiyano@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>