Access points' "PropertiesChanged" dbus signals freeze UI on mobile devices

This bug was tracked at:
https://bugs.launchpad.net/unity8/+bug/1480877
and has to do with the network-manager bearer plugin.

"I've been trying to track down the cause of the occasional UI freezes on my Krillin device, and I noticed that whenever the UI freezes for 2-4 seconds, I get a burst of "PropertiesChanged" signals in dbus-monitor

Here's a log of what's shown in dbus-monitor: http://pastebin.ubuntu.com/11992322/

I'd guess the problem is in the code that actually catches the signals and acts accordingly.

HOW TO REPRODUCE:
1) Move to a place where many wifi hotspots are available
2) Connect the device via USB and run "phablet-shell" and then "dbus-monitor"
3) Use the device while keeping an eye on dbus-monitor output"