amd-xgbe: Set RSS enablement based on hardware features

The RSS support requires enablement based on the features reported by
the hardware. The setting of this flag is missing. Add support to
set the RSS enablement flag based on the reported hardware features.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>