ipv6: discard fragment queue earlier if there is malformed datagram

ipv6: discard fragment queue earlier if there is malformed datagram

Currently the kernel IPv6 implementation is not dicarding the fragment
queue upon receiving a IPv6 fragment that is not 8 bytes aligned. It
relies on queue expiration to free the queue.

While RFC 8200 section 4.5 does not explicitly mention that the rest of
fragments must be discarded, it does not make sense to keep them. The
parameter problem message is sent regardless that. In addition, if the
sender is able to re-compose the datagram so it is 8 bytes aligned it
would qualify as a new whole datagram not fitting into the same fragment
queue.

The same situation happens if segment end is exceeding the IPv6 maximum
packet length. The sooner we can free resources the better during
reassembly, the better.

Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
Link: https://patch.msgid.link/20260225133758.4553-1-fmancera@suse.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>