drivers: wifi: simplelink: Add handling for unknown root CA
drivers: wifi: simplelink: Add handling for unknown root CA

Error code SL_ERROR_BSD_ESECUNKNOWNROOTCA is returned from sl_Connect()
when the root CA used is not part of the certificate catalog on the
network processor. We should warn the users about this and continue on,
given the connection is successful.

Signed-off-by: Vincent Wan <0da4a49376daf88459b96a63301ecd5aff2f3b80@linaro.org>

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