dccp: remove unnecessary codes in ipv6.c

commit 0979e465

 upstream.

opt always equals np->opts, so it is meaningless to define opt, and
check if opt does not equal np->opts and then try to free opt.

Signed-off-by: RongQing.Li <roy.qing.li@gmail.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>