net: lwm2m: Fix PULL FW update in case of URI parse errors
net: lwm2m: Fix PULL FW update in case of URI parse errors

The memset on firmware_ctx during PULL FW update initialization will
set the socket descriptor to a valid value of 0. This leads to an error
if parsing of the URI provided by the server fails, and the firware_ctx
is closed - the socket with a descriptor 0 will be accidently closed.
Fix this by invalidating the socket FD after the memset on
initialization.

Signed-off-by: Robert Lubos <9d28997c6894a2d0321a7bb399169af7ce99b64e@nordicsemi.no>

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