net/sched: flower: Add PPPoE filter

Add support for PPPoE specific fields for tc-flower.
Those fields can be provided only when protocol was set
to ETH_P_PPP_SES. Defines, dump, load and set are being done here.

Overwrite basic.n_proto only in case of PPP_IP and PPP_IPV6,
otherwise leave it as ETH_P_PPP_SES.

Signed-off-by: Wojciech Drewek <wojciech.drewek@intel.com>
Acked-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>