ethdev: add PPPoE RSS offload types

ethdev: add PPPoE RSS offload types

This patch defines new RSS offload types for PPPoE. Typically,
session id would be the RSS input set for a PPPoE packet, but
as a hint, each driver may have different default behaviors.

Signed-off-by: Simei Su <simei.su@intel.com>
Reviewed-by: Qi Zhang <qi.z.zhang@intel.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>