We can have an update pending because it's too fast, but
refresh_local_channel is supposed to make sure we're up-to-date, so
force immediate application in that case.
Otherwise, we call update_local_channel at the bottom which frees the
pending update. This can mean that we miss a change in fees, for example.
Changelog-Fixed: errors: Errors returning a `channel_update` no longer return an outdated one.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>