s3-smbd Don't send SPNEGO principal (rfc4178 hint) by default

s3-smbd Don't send SPNEGO principal (rfc4178 hint) by default

This patch, based on the suggestion by Goldberg, Neil R. <ngoldber@mitre.org>
turns off the sending of the principal in the negprot by default, matching
Windows 2008 behaviour.

This slowly works us back from this hack, which from an RFC
perspective was never the right thing to do in the first place, but we
traditionally follow windows behaviour.  It also discourages client
implmentations from relying on it, as if they do they are more open to
man-in-the-middle attacks.

Andrew Bartlett
(cherry picked from commit b3c2df5e0d0ba1c17c3248bf9d238de3c54613ef)