Fix frequency range reporting and display for 900MHz & 3GHz devices

[aanon4]

Thanks to @pmilazzo for helping debug this.

[k6ccc]

What's supposed to be different on this one? I updated all three of my Rocket M3 nodes to NB 2588 and don't see any difference. Or did this only affect 900 MHz devices despite the name?

Also, reminder to please add the release date on releases so the date shows up on the change log. Really makes it easier to tell what is new when there are lots of changes happening.

[pmilazzo]

Jim:

The PR changes two things: the "Channel" value displayed on the Node Status page (the node's home page) and the values in the "Channel" selector box on the Basic Setup tab. Both should now contain only the frequency in MHz and not the (misleading) channel number.

Also, the previous nightly build would allow you to choose inappropriate (out of band) frequencies; it is now limited to appropriate choices.

I have not been able to test this version on my M3 nodes because we are currently experiencing a network partition and all my M3 nodes are in the other half. Thus, it would be helpful if you could verify that your displayed frequencies are correct.