net: ipv6: Do not pass ICMPv6 packets to net_conn_input
net: ipv6: Do not pass ICMPv6 packets to net_conn_input

ICMPv6 network packets are processed and consumed (if not dropped)
within `net_icmpv6_input` function. Therefore they shoud not be
passed to the `net_conn_input` function.

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

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