clang-format c++ code

include/grpc++/async_generic_service.h

include/grpc++/async_unary_call.h

include/grpc++/byte_buffer.h

include/grpc++/channel_interface.h

include/grpc++/client_context.h

include/grpc++/completion_queue.h

include/grpc++/config.h

include/grpc++/credentials.h

include/grpc++/generic_stub.h

include/grpc++/impl/call.h

include/grpc++/impl/client_unary_call.h

src/cpp/client/channel.h

src/cpp/client/channel_arguments.cc

src/cpp/client/client_context.cc

src/cpp/client/client_unary_call.cc

src/cpp/client/create_channel.cc

src/cpp/client/secure_credentials.cc

src/cpp/proto/proto_utils.cc

src/cpp/proto/proto_utils.h

src/cpp/server/async_generic_service.cc