AsyncMessenger: Avoid join when worker thread not started

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
AsyncConnection: Avoid seq ack not send and skip sd<0 shutdown

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
AsyncConnection: Rescheduler write event when connect successfully

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
AsyncConnection: Fix mark_down problem when calling send_message

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
AsyncMessenger: move Async* related file to msg/async

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
AsyncMessenger: Fix header file path

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
AsyncMessenger: add copyright for async files

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
AsyncMessenger: add comments for structures

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
AsyncMessenger: Remove unused option

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>