Subband selection

The updates seem to not allow for a selection of a subband in a few channel plans, is this possible at all?

It seemed to work on sub band 1 ok with the pr i pushed before your updates, I would look into it more but my rustacean is not very high :D

I tried server as au915_1 in case this made a difference but it still throws from all 8 bands now which is suboptimal for LNS testing.

```
region = "AU915"
packet_forwarder = "pf_one"
server = "au915_1"
...
```
> I haven't tried anything on the region setting yet*

Reproduce the failure with region = "AU915" and server = "au915_1", then trace the channel-plan and subband-selection handling for the eight bands. Done means the affected channel plans accept a selected subband and no longer throw during LNS testing.

Written by the indexing model from the issue text.