[Samba] dns_tkey_negotiategss: TKEY is unacceptable - documentation update

[Peter Serbe]

Hi list, 

I have struggled with one of my DCs, which persistently refused to do DNS updates, 
even after I carefully went through all the actions listed in the wiki page: 

https://wiki.samba.org/index.php/Dns_tkey_negotiategss:_TKEY_is_unacceptable

Finally I found the reason: The resolv.conf on the DC pointed to itself, so that 
I might have hit the DNS islanding trap. After pointing the primary entry in 
resolv.conf to the main DC the DNS update immediately was working. 

Maybe the wiki should give a hint on checking the name resolver, too. 

Best regards
Peter