One is called on every plugin return, and tells us whether to continue;
the other is only called if every plugin says ok.
This works for things like payload replacement, where we need to process
the results from each plugin, not just the final one!
We should probably turn everything into a chained callback next
release.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
They callback must take ownership of the payload (almost all do, but
now it's explicit).
And since the payload and cb_arg arguments to plugin_hook_call_() are
always identical, make them a single parameter.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
