NULL pointer dereference in the BSD raw IPv6 send path when the destination table is full

In Eclipse ThreadX NetX Duo versions 6.0 through 6.5.2.202603a, built with BSD raw socket and IPv6 support, the IPv6 raw send path uses the destination-table entry it adds without checking that the add succeeded. When the destination table is full and an off-link destination is reached through a default router whose neighbour cache entry is unknown, sending on an IPv6 raw socket with header inclusion dereferences a NULL pointer; a remote sender can fill the table, for example with ICMPv6 Packet Too Big messages, and crash the sending thread.