Buffer Over-read when receiving improperly sized ICMPv6 packets in FreeRTOS-Plus-TCP

A missing validation check in FreeRTOS-Plus-TCP's ICMPv6 packet processing code can lead to an out-of-bounds read when receiving ICMPv6 packets of certain message types which are smaller than the expected size. These issues only affect applications using IPv6. Users should upgrade to the latest version and ensure any forked or derivative code is patched to incorporate the new fixes.