lnwallet/channel: check validity of received commitPoint
lnwallet/channel: check validity of received commitPoint

This commit adds a check for the LocalUnrevokedCommitPoint sent to us by
the remote during channel reestablishment, ensuring it is the same point
as they have previously sent us.

LightningNetwork/lnd,aakselrod/lnd,aakselrod/lnd,LightningNetwork/lnd