net: lwm2m: Fixed crash at LwM2M registration timeout
net: lwm2m: Fixed crash at LwM2M registration timeout

LwM2M context close moved to thread safe place when RD client
run state machine.

Signed-off-by: Juha Heiskanen <da286ad296b3dcaa6fdad737a1ad7c3ff3e427db@nordicsemi.no>

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