Updating a TXT field by advertising an existing target does not work

Created by: stephanemagnenat

Commit 0012396f adds support for the busy flag in dummynode, that should be set to true (and thus present in the TXT flag) if the target is being used.

While the call Zeroconf::advertise() is called with the updated TxtRecord, the description received by the client (for instance asebatargetlist-thread) is not updated.