[RFE] Allow filtering out unrelevent devices in 'Permit join' menu

[bagasse]

As a user, I want to display only some devices in 'Permit join' menu. Some devices (like light bulb) can be used as router but are behind a eletric switch and so not always available but are displayed as router option for 'Permit join' menu. It would be nice if we can filter out this kind of devices so only relevant devices will be listed in the menu (eg via a regexp setting to filter out devices names patterns)