We used to send our tx_sigs before we got to channeld existing. We
changed how this worked so that multifundchannel could live, but failed
to clean up the logic of what "having a psbt around" means wrt channeld
and messaging our peer.
The general idea is that we want to send `tx_signatures` to our peer on
reconnect until they've sent us `funding_locked`.
Note that it's an error to
- send `funding_locked` without having sent `tx_signatures`
- send `tx_signatures` after sending `funding_locked`
We use the 'finalized' state of the peer's inputs/outputs to help signal
where we are in receiving their sigs -- but this doesn't work at all for
opens where the peer doesn't contribute inputs at all.
This isn't really a huge deal, but it does mean that if we receive a
peer's `tx_sigs` more than once (will happen for a reconnect before
`funding_locked`), then we'll issue a notification about receiving their
sigs multiple times. /shrug
niftynei
1b3a9be416