net: mvpp2: cls: Extract the RSS context when parsing the ethtool rule

ethtool_rx_flow_rule_create takes into parameter the ethtool flow spec,
which doesn't contain the rss context id. We therefore need to extract
it ourself before parsing the ethtool rule.

The FLOW_RSS flag is only set in info->fs.flow_type, and not
info->flow_type.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>