Support multiple ports in gRPC Java server

[fiower]

Please answer these questions before submitting your issue.

What version of gRPC are you using?

Most recent

What did you expect to see?

Support multiple ports in gRPC Java server.

[zpencer]

@fiower can you provide more context about what problem you're trying to solve by exposing multiple ports?

[carl-mastrangelo]

Multiple ports is common inside google. The C implementation of gRPC Java supports it already.