use NLRI on MP_REACH

.gitignore

protocols/bgp/packet/decoder.go

protocols/bgp/packet/decoder_test.go

protocols/bgp/packet/mp_reach_nlri.go

protocols/bgp/packet/mp_reach_nlri_test.go

protocols/bgp/packet/nlri.go

protocols/bgp/packet/nlri_test.go

protocols/bgp/packet/path_attributes_test.go

protocols/bgp/server/fsm_address_family.go

protocols/bgp/server/update_helper_test.go

protocols/bgp/server/update_sender.go