connectd is the only user of the cryptomsg async APIs; better to
open-code it here. We need to expose a little from cryptomsg(),
but we remove the 'struct peer' entirely from connectd.
One trick is that we still need to defer telling lightningd when a
peer reconnects (until it tells us the old one is disconnected). So
now we generate the message for lightningd and send it once we're woken.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
