KCC: fix is_bridgehead_failed() according to documentation

KCC: fix is_bridgehead_failed() according to documentation

Throughout the KCC specification `detectFailedDCs` is documented along
the lines of "true to detect failed DCs", and it gets passed down to
this function. And what do we see here? It is used as a default value
when a stale link is not detected. That is entirely different. So who is
right -- the comments or the pseudo-code?

This commit follows the comments. It works!

   Documentation 1,  Pseudo-code 0

See [MS-ADTS] — v20140502, section 6.2.2.3.4.4, page 569.

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Garming Sam <garming@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>