ath: Add regulatory mapping for FCC3_ETSIC

ath: Add regulatory mapping for FCC3_ETSIC

The regdomain code is used to select the correct the correct conformance
test limits (CTL) for a country. If the regdomain code isn't available and
it is still programmed in the EEPROM then it will cause an error and stop
the initialization with:

  Invalid EEPROM contents

The current CTL mappings for this regdomain code are:

* 2.4GHz: ETSI
* 5GHz: FCC

Signed-off-by: Sven Eckelmann <sven.eckelmann@openmesh.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>