[Samba] invalid value 'netbios backup domain controller'

[Ken Bass]

I have been having issues with my Centos 7 Samba4 setup. Not sure if it 
is related to a recent samba package/version update, but things are no 
longer very stable.
While looking at the logs, I see the following message on my BDC.

WARNING: Ignoring invalid value 'netbios backup domain controller' for 
parameter 'server role'

This worked before and is consistent with the man page for the smb.conf 
file, so I am confused.

My PDC is listed as 'classic primary domain controller' which does not 
generate an error message.