[DCCPv6]: Add a FIXME for missing IPV6_PKTOPTIONS

This refers to the possible memory leak pointed out in
http://www.mail-archive.com/dccp@vger.kernel.org/msg00574.html,
fixed by David Miller in
http://www.mail-archive.com/netdev@vger.kernel.org/msg24881.html



and adds a FIXME to point out where code is missing.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>