Fix breakage to target mode support.

Fix breakage to target mode support.

What we'd like to know is whether or not we have a listener
upstream that really hasn't configured yet. If we do, then
we can give a more sensible reply here. If not, then we can
reject this out of hand.

Choices for what to send were
	Not Ready, Unit Not Self-Configured Yet
	(0x2,0x3e,0x00)
for the former and
	Illegal Request, Logical Unit Not Supported
	(0x5,0x25,0x00)
for the latter.

We used to decide whether there was at least one listener
based upon whether the black hole driver was configured.

However, recent config(8) changes have made this hard to do
at this time.

Actually, we didn't use the above quite yet, but were sure considering it.