net: ipv6: Fix crash from fragmented packets
net: ipv6: Fix crash from fragmented packets

Echo server crashes upon reception of fragmented packets. This
occurs when fragmentation is enabled with the default prj.conf
of echo server. The cause is that by default with logs disabled
net_sprint_ipv6_addr returns NULL.

Signed-off-by: Ruslan Mstoi <348dc8e8f10581f5bc17672b9c406a6d9fcc1430@intel.com>

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