add channelized frequency and signal level to acars output

[rpatel3001]

for use with https://github.com/rpatel3001/docker-gr-iridium-toolkit and https://github.com/sdr-enthusiasts/docker-acarshub

[Sec42]

Can you provide some more reason/rationale for this? The channelize is a "guess" - it will be off by +/- 1 channel due to doppler shift, so I don't think it is very useful to propagate that to users.

[rpatel3001]

I just like having the data in my acarshub stats and I think others will too.

Also, I think having a +/- 1 channel frequency guess is better than not having any frequency data.

[Sec42]

I'd rather propagate the raw frequency than a "wrong" channel. Would that be acceptable for you?

[rpatel3001]

That would be fine, we can channelize externally (to limit how long the frequency list in acarshub gets)

I can update the PR in a bit.

[rpatel3001]

good to merge?