Remove RSS support in ENA

Receive Side Scaling is optional feature that could be enabled in kernel
configuration by defining flag RSS.

Kernel uses hash to store and find protocol control block which is
stored in hash tables.
Kernel and NIC hash functions must be consistent. Otherwise case lookup
fails.

To achieve this kernel provides API to set proper hash key to NIC.
As it is not possible to change key for virtual ENA NIC, this driver
cannot support RSS function.

ENA is designed to work in virtual environments so supporting hardware
version of this card is unnecessary.

Submitted by: Rafal Kozik <rk@semihalf.com>
Obtained from: Semihalf
Sponsored by: Amazon, Inc.