Refactor IP versioning in API

apps/bmp-streamer/client/main.go

apps/bmp-streamer/pkg/apiserver/server.go

net/api/net.proto

net/ip.go

net/ip_test.go

net/prefix.go

net/prefix_test.go

route/api/route.proto

route/bgp_path.go

route/bgp_path_test.go

route/path.go