[chirp_users] Kenwood TM-281a works, too

The Kenwood TM-271A appears on the Supported Radio Models list.

I have just hooked up a TM-281A (newer model of the same radio) to the stable release and it appears to work fine. IDed by chirp as a 271 and works in "live mode" like the 271.

If there is anything I should test before adding it to the Supported list let me know.