This works enough to exchange data with my openwrt ath9k AP
running GCMP-128 and GCMP-256.
The AES-GCMP code is BSD licenced code from hostapd.git .
Note - this is a WIP commit just so the code isn't lost in the sands of time. There is a bunch of clean-up to do and perhaps some code de-duplication with the CCMP crypto module, as well as TODO items in GCMP/CCMP around the AAD header contents.
I'd honestly also prefer the AES-GCM code to be located elsewhere (and the AES-CCM too for that matter), but not necessarily to use the crypto framework. That way other projects wanting to port net80211 can port it without also needing to port the crypto framework just for working AES-GCM.