Prevent serving TLS via ports.grpc
We remove the ability to run the ports.grpc in TLS mode to avoid
confusion and to simplify configuration. This breaking change
ensures that any user currently using ports.grpc in an encrypted
mode will receive an error message indicating that ports.grpc_tls
must be explicitly used.
The suggested action for these users is to simply swap their ports.grpc
to ports.grpc_tls in the configuration file. If both ports are defined,
or if the user has not configured TLS for grpc, then the error message
will not be printed.
