Fixing tests and adding basic capablities support (packet layer)

config/peer.go

main.go

protocols/bgp/packet/bgp.go

protocols/bgp/packet/decoder.go

protocols/bgp/packet/decoder_test.go

protocols/bgp/packet/encoder.go

protocols/bgp/packet/encoder_test.go

protocols/bgp/packet/parameters.go

protocols/bgp/packet/path_attributes.go

protocols/bgp/packet/path_attributes_test.go

protocols/bgp/server/fsm.go

protocols/bgp/server/peer.go

routingtable/adjRIBOutAddPath/adj_rib_out_add_path.go