Feature Request - Add a dialog to the channel page to make it more obvious when default modem settings have changed

[b8b8]

Add an indicator to the channel page to show the current channel and frequency so it is more obvious when adding LongFast etc. as a secondary channel that the frequency slot has changed from defaults which may not be caught when doing initial channel setup.

[andrekir]

let's present a dialog explaining to the user when the frequency changes.