internal/transport: do not mask ConnectionError (#4561)
internal/transport: do not mask ConnectionError (#4561)


grpc/grpc-go,stanley-cheung/grpc-go,menghanl/grpc-go,stanley-cheung/grpc-go,menghanl/grpc-go,dfawley/grpc-go,grpc/grpc-go,dfawley/grpc-go