Work around lnd sending funding_locked before channel_reestablish

[TheBlueMatt]

It doesn't look likely that lnd is going to fix lightningnetwork/lnd#4006 at any point, really, so we need to work around it. C-lightning apparently has a similar workaround, where they store the funding_locked until they receive a channel_reestablish, and then deliver the funding_locked after the fact. We could do something similar in the PeerHandler (which is a bit awkward, but also maybe the simplest place, and anywhere is awkward), or allow such nonsensical message ordering all the way down at the channel level.