sm: Fix dirmngr loadcrl for intermediate certs

* sm/call-dirmngr.c (run_command_inq_cb): Support ISTRUSTED.
(inq_certificate): Distinguish unsupported inquiry error.

When loading a CRL through "gpgsm --call-dirmngr loadcrl foo"
dirmngr can ask gpgsm back if a certificate used ISTRUSTED, which
previously resulted in an error.