Wait for channels to be restored before initiating splice-in

[t-bast]

We must defer splice-in operations until channels have been restored, otherwise the splice will be skipped until the next block is found or the wallet restarts. We currently wait for all channels to be up or for 10 seconds, because we want to ignore "zombie" new channels that haven't been fully signed.

This isn't ideal: it would be better if we had a robust way of knowing that all channels that can be reestablished have been reestablished. We should exchange information with our peer to know what channels they expect to reestablish, which would let us know what to expect.

[t-bast]

Done in #659