Instead of indicating where to place the fd, you say how many: the
fd array gets passed into the callback.
This is also clearer for the users.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This uses a single fd for both status and control.
To make this work, we enforce the convention that replies are the same
as requests + 100, and that their name ends in "_REPLY".
This also means that various daemons can simply exit when done; there's
no race between reading request and closing status fds.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
