add data type identifier method to AprsData

[ta3pks]

In my usecase aprs messages gets filtered by the data type however once parsed this information was gone in aprs_parser.
Before this pr only way to get this information was to manually reparsing package

[scd31]

Hi!

First off, thanks for the PR and sorry it took me so long to get to it. I didn't have notifications turned on (a problem which has since been fixed) and didn't see it until a few days ago.

Just wondering, what's the use-case for this?

One potential issue is that when creating a new AprsPacket, the user will have to fill in these new fields. This may be confusing to someone not familiar with the standard, plus the value specified doesn't have any effect on encoding

[ta3pks]

hi thanks for the response.
here you can see this makes filtering a lot easier. I could achieve this by using another function but the problem with that is that this information is already there at the time of parsing and just goes to waste then we need to do some other operation to get it again back.

Ps. the link i shared belongs to the program i wrote named aprs-agent which can cross reference multiple networks such as aprs > email or aprs > twitter etc

[scd31]

Is there a reason you want to treat 0x1c and the backtick differently, for example? Or are you just intending to use this as a proxy between the different APRS packet types? The latter is preferable imo, since it could be implemented via a method on AprsData that doesn't require a new field.