samples: lwm2m: allow longer endpoint names
samples: lwm2m: allow longer endpoint names

Server might return the endpoint name in a registration reply. Default
max allowed endpoint name is only 12 characters.

Signed-off-by: Veijo Pesonen <cb89a3750227d52d34160f03c031368aef19d3be@nordicsemi.no>

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