Set the next message to send.
If no message can currently be set (perhaps because the previous one is not yet done being sent), returns false, and msg will be unmodified. Otherwise msg is enqueued (and possibly moved-from) and true is returned.
true if the message was accepted, false if none could be set right now.
| Name | Description |
|---|---|
| msg [inout] | the message to enqueue; may be moved-from on success. |