libnm: add "Since:" annotation to NM_WIFI_DEVICE_CAP_FREQ_6GHZ
Summary
The enum value is public API; indicate when it was introduced.
Fixes: 8f438d8d ('wifi: add 6ghz device capability flag')
The enum value is public API; indicate when it was introduced.
Fixes: 8f438d8d ('wifi: add 6ghz device capability flag')