installed-fresh --input-fnkeys FLAGS (with --input) appends the guest
boot-arg snap_i2c_fnkeys=FLAGS, which a SnapI2CHID built with
SNAP_I2C_HID_FNKEYS (PROFILE=desktop-fnkeys) reads; other builds
ignore it. The sets the kext would refuse are refused here: 0, bits
above 0x1f, brightness encoding 3, the host Fn-lock (0x4) without
translation (0x1), an encoding alone. Without the option the boot
argument addition is unchanged.
python3 tools/test-input-fnkeys.py: 4 tests OK;
python3 tools/test-zone-log.py: 4 tests OK.