Move channel restoration after monitor update to a two-part macro

Move channel restoration after monitor update to a two-part macro

The channel restoration code in channel monitor updating and peer
reconnection both do incredibly similar things, and there is
little reason to have them be separate. Sadly because they require
holding a lock with a reference to elements in the lock, its not
practical to make them utility functions, so instead we introduce
a two-step macro here which will eventually be used for both.

Because we still support pre-NLL Rust, the macro has to be in two
parts - one which runs with the channel_state lock, and one which
does not.