net: coap: coap_next_token single sys_rand_get call
net: coap: coap_next_token single sys_rand_get call

Improve coap_next_token by using a single sys_rand_get call.

Signed-off-by: Pieter De Gendt <b5b50e3ea5dc0014327690ec78e146f3b45ee870@basalte.be>

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