* Updates to the channel are made atomic, and consistent via a proxy
object: “ChannelUpdate” which encapsulates an update transaction. Only
one update transaction may be outstanding at any time.
* Update transactions are initiated via AddHTLC or SettleHTLC.
* Once a transaction has been begun, in order to complete the update
the transaction must first be presented with a signature from the
counter-party for our new version of the commitment tx
(VerifyNewCommitmentSigs), and finally to atomically commit the
transaction, the counterparty’s pre-image to their previous revocation
hash must be validate (Commit).