net: lwm2m: Fix LwM2M resume from Update registration state
net: lwm2m: Fix LwM2M resume from Update registration state

If LwM2M engine was paused at ENGINE_UPDATE_SENT it was not
able to resume lwm2m engine properly. There was also missing
RD client Pending message free which could also affect a issue.

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

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