Fix re-sending commitment updates with an outbound fee update

Fix re-sending commitment updates with an outbound fee update

When we send an update_fee to our counterparty on an outbound
channel, if we need to re-send a commitment update after
reconnection, the update_fee must be present in the re-sent
commitment update messages. However, wewere always setting the
update_fee field in the commitment update to None, causing us to
generate invalid commitment signatures and get channel
force-closures.

This fixes the issue by correctly detecting when an update_fee
needs to be re-sent, doing so when required.