sctp: do not leak chunks that are sent to unconfirmed paths

Currently, if a chunk is scheduled to be sent through a transport that
is currently unconfirmed, it will be leaked as it is dequeued from outq
and is not re-queued nor freed.

As I'm not aware of any situation that may lead to this situation, I'm
fixing this by freeing the chunk and also logging a trace so that we can
fix the other bug if it ever happens.

Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>