Insteon: ALDB_PLM sub add_link improperly sets message callback

[krkeegan]

Similar to Issue #61 which was solved in pull request #63.

The sub add_link in the aldb_plm object sets the $message->callback to _process_sync_queue. This results in _process_sync_queue getting called twice, once when the message is sent, and then again when the ACK is processed. This causes sync_links to process out of order.