Async notifier for channel creation process.
Function using this handler:
This handler allows you to define a notify function that will be called once the channel is created or something have failed with errors such as timeout reached or channel creation process failures.
If something fails, a -1 will be received on channel_num and channel will be NULL. Otherwise, you will received the channel number created and a reference to channel created. It is not needed to hold a reference to channel. You can get it by using vortex_connection_get_channel.