AsyncMessenger: Use unordered_map instead of map and remove unused codes

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
AsyncMessenger: Check send queue when message in queue before connect ready

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
AsyncConnection: Rescheduler avoid dead lock

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