Count intro circuit and not only established ones

When cleaning up extra circuits that we've opened for performance reason, we
need to count all the introduction circuit and not only the established ones
else we can end up with too many introduction points.

This also adds the check for expiring nodes when serving an INTRODUCE cell
since it's possible old clients are still using them before we have time to
close them.

Signed-off-by: David Goulet <dgoulet@ev0ke.net>