If channeld dies for some reason (eg, reconnect) and we didn't yet announce
the channel, we can miss doing so. This is unusual, because if lightningd
restarts it rearms the callback which gives us funding_locked, so it only
happens if just channel dies before sending the announcement message.
This problem applies to both temporary announcement (for gossipd) and
the real one. For the temporary one, simply re-send on startup, and
remote the error msg gossipd gives if it sees a second one. For the
real one, we need a flag to tell us the depth is sufficient; the peer
will ignore re-sends anyway.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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