net: openthread: handle NONE level logs
net: openthread: handle NONE level logs

`OT_LOG_LEVEL_NONE` has some uses within OpenThread but it is not
hanled in the Zephyr's platform implementation. This commit makes
use of those logs as `LOG_LEVEL_ERR` level.

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

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