After getting confirmation from Guenther, add 3 changes we'll

After getting confirmation from Guenther, add 3 changes we'll
ultimately need to fix bug #6099 Samba returns incurrate capabilities list.
1). Add a comment to point out that r->in.negotiate_flags is an aliased pointer to
r->out.negotiate_flags.
2). Ensure we return NETLOGON_NEG_STRONG_KEYS in our flags
return if the client requested it.
3). Clean up the error exits so we always return the same
way.
Signed off by Guenther.
Jeremy.
(cherry picked from commit 78fb479325ce7073ab8383ada3903080d12aef91)