The current code sends hsmstatus_client_bad_request via the req fd;
this won't work, since lightningd uses that synchronously and only
expects a reply to its commands. So send it via status_conn.
We also enhance hsmstatus_client_bad_request to include details, and
create convenience functions for it. Our previous handling was ad-hoc;
we sometimes just closed on the client without telling lightningd,
and sometimes we didn't tell lightningd *which* client was broken.
Also make every handler the exact same prototype, so they now use the
exact same patterns (hsmd *only* handles requests, makes replies).
I tested this manually by corrupting a request to hsmd.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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