net: tests: Fix coap test case
net: tests: Fix coap test case

Test case should first check for next block in the coap packet and
unref the packet (assuming packet has been sent).

Signed-off-by: Ravi kumar Veeramally <406c082aeb452858c41b213a757768e1c1dff29e@linux.intel.com>

punitvara/zephyr,galak/zephyr,kraj/zephyr,kraj/zephyr,kraj/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,nashif/zephyr,finikorg/zephyr,galak/zephyr,zephyriot/zephyr,nashif/zephyr,galak/zephyr,finikorg/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,galak/zephyr,kraj/zephyr,punitvara/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,zephyriot/zephyr,zephyriot/zephyr,finikorg/zephyr,zephyriot/zephyr,punitvara/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,Vudentz/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,explora26/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,mbolivar/zephyr,explora26/zephyr,Vudentz/zephyr,mbolivar/zephyr,ldts/zephyr,mbolivar/zephyr,mbolivar/zephyr,kraj/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,punitvara/zephyr,Vudentz/zephyr,ldts/zephyr,Vudentz/zephyr,ldts/zephyr,mbolivar/zephyr,punitvara/zephyr,zephyriot/zephyr,nashif/zephyr