Buffer Over-read when receiving IPv6 packets with incorrect payload length in FreeRTOS-Plus-TCP

A missing validation check in FreeRTOS-Plus-TCP's IPv6 packet processing code can lead to an out-of-bounds read when receiving a IPv6 packet with incorrect payload lengths in the packet header. This issue only affects applications using IPv6. We recommend users upgrade to the latest version and ensure any forked or derivative code is patched to incorporate the new fixes.