Filter match: MPLS: Header metadata: forwarding-class, loss-priority

This feature enables the matching of the MPLS header metadata fields bind to the WAN interface, with the following options: - forwarding-class value: Match the forwarding class of the MPLS packet metadata value. - forwarding-class-except value: Do not match the forwarding class of the MPLS packet metadata value. - loss-priority value: Match the loss priority of the MPLS packet metadata value. - loss-priority-except value: Do not match the loss priority of the MPLS packet metadata value.