e41e756 removed
`ChannelManager::send_payment_with_route` due to a rebase error as
it was originally written when `send_payment_with_route` had been
made test-only.

Here we restore it to be public.

e41e756 introduced some
indentation errors that we fix here.

e41e756 started exposing some
tests but left some functions as non-pub that were now pub (though
it doesn't actually matter as we expose the function pointers
directly via `inventory).