dpaa2-eth: Make Rx flow hash key configurable

Until now, the Rx flow hash key was a 5-tuple (IP src, IP dst,
IP nextproto, L4 src port, L4 dst port) fixed value that we
configured at probe.

Add support for configuring this hash key at runtime.
We support all standard header fields configurable through ethtool,
but cannot differentiate between flow types, so the same hash key
is applied regardless of protocol.

We also don't support the discard option.

Signed-off-by: Ioana Radulescu <ruxandra.radulescu@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>