[3540][UI][core] Fix interface not being updated in thinclient

[DjLegolas]

When changing the interface in both GTK and ConsoleUI, we call directly to deluge.common.is_interface, which checks the interface on the local machine and not on the daemon's machine.

The WebUI does not seem to have any validation on input.

closes: https://dev.deluge-torrent.org/ticket/3540

[cas--]

Ah yes I encountered this issue!

Will need to handle backward compatibility in the client for daemons that don't have that method exported

[DjLegolas]

depends on: #427