In the case where we can't decrypt the onion, we can't fail it in the
normal way (which is encrypted using the onion shared secret), we need
to respond with a update_fail_malformed_htlc message.
Moreover, we need to remember this for persistence. This means that
we really have three conclusions for an HTLC: fulfilled, failed,
malformed. Fix up the logic everywhere which assumed failed or
fulfilled.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Rusty Russell