add PBB support
fix MPLS operations

* make parse_mpls parse multiple mpls shims
* make use of mpls_header_t
* mpls push tag sets ethertype
* fix unittests to use new packet_info members
add PBB support
fix MPLS operations

* make parse_mpls parse multiple mpls shims
* make use of mpls_header_t
* mpls push tag sets ethertype
* fix unittests to use new packet_info members
Merge branches 'pbb_and_mpls' and 'pbb_and_mpls' of https://github.com/iHiroakiKawai/trema-edge into pbb_and_mpls
Merge branch 'pbb_and_mpls' of https://github.com/iHiroakiKawai/trema-edge into iHiroakiKawai-pbb_and_mpls