net: route: Do not try to access null link layer address
net: route: Do not try to access null link layer address

In some cases the lladdr might not be set, currently this is
seen with RPL unit tests, in which case we must not access
the lladdr.

Jira: ZEP-2330

Signed-off-by: Jukka Rissanen <f9f077d1da4c7aa947f9864fa5a28c3588f6a45d@linux.intel.com>

aceofall/zephyr-iotos,zephyrproject-rtos/zephyr,explora26/zephyr,kraj/zephyr,zephyriot/zephyr,fbsder/zephyr,punitvara/zephyr,finikorg/zephyr,explora26/zephyr,ldts/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,holtmann/zephyr,mbolivar/zephyr,holtmann/zephyr,nashif/zephyr,galak/zephyr,explora26/zephyr,punitvara/zephyr,kraj/zephyr,fbsder/zephyr,kraj/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,kraj/zephyr,ldts/zephyr,Vudentz/zephyr,punitvara/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,zephyriot/zephyr,fbsder/zephyr,finikorg/zephyr,zephyriot/zephyr,punitvara/zephyr,nashif/zephyr,nashif/zephyr,explora26/zephyr,runchip/zephyr-cc3220,ldts/zephyr,aceofall/zephyr-iotos,runchip/zephyr-cc3220,runchip/zephyr-cc3220,aceofall/zephyr-iotos,mbolivar/zephyr,rsalveti/zephyr,Vudentz/zephyr,punitvara/zephyr,galak/zephyr,rsalveti/zephyr,ldts/zephyr,fbsder/zephyr,aceofall/zephyr-iotos,zephyriot/zephyr,Vudentz/zephyr,runchip/zephyr-cc3220,fbsder/zephyr,Vudentz/zephyr,aceofall/zephyr-iotos,mbolivar/zephyr,runchip/zephyr-cc3220,rsalveti/zephyr,holtmann/zephyr,rsalveti/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,mbolivar/zephyr,zephyrproject-rtos/zephyr,holtmann/zephyr,GiulianoFranchetto/zephyr,mbolivar/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,kraj/zephyr,nashif/zephyr,holtmann/zephyr,rsalveti/zephyr,finikorg/zephyr,Vudentz/zephyr,ldts/zephyr,galak/zephyr,zephyriot/zephyr