Invalid Pointer Dereference when receiving UDP/IPv6 packets in FreeRTOS-Plus-TCP

A missing validation check in FreeRTOS-Plus-TCP's UDP/IPv6 packet processing code can lead to an invalid pointer dereference when receiving a UDP/IPv6 packet with an incorrect IP version field in the packet header. This issue only affects applications using IPv6. We recommend upgrading to the latest version and ensure any forked or derivative code is patched to incorporate the new fixes.