net: openthread: fix error codes for TX done
net: openthread: fix error codes for TX done

Fix potential bug when returning error codes not handled by
OpenThread in `otPlatRadioTxDone`.

Signed-off-by: Eduardo Montoya <c6d924925ebf82d772472f7877e771cedf439387@nordicsemi.no>

galak/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr