Workaround lnd sending funding_locked before channel_reestablish

Workaround lnd sending funding_locked before channel_reestablish

lnd has a long-standing bug where, upon reconnection, if the
channel is not yet confirmed they will not send a
channel_reestablish until the channel locks in. Then, they will
send a funding_locked *before* sending the channel_reestablish
(which is clearly a violation of the BOLT specs). We copy
c-lightning's workaround here and simply store the funding_locked
message until we receive a channel_reestablish.

See-also https://github.com/lightningnetwork/lnd/issues/4006

Fixes #963