s3:smb2_sesssetup: check session_info security level before it gets talloc_move'd

s3:smb2_sesssetup: check session_info security level before it gets talloc_move'd

We talloc_move() session_info to session->global->auth_session_info
which sets session_info to NULL.

This means security_session_user_level(NULL, NULL) will always return
SECURITY_ANONYMOUS so we never sign the session setup response.

Bug: https://bugzilla.samba.org/show_bug.cgi?id=13661

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>
Autobuild-User(master): Ralph Böhme <slow@samba.org>
Autobuild-Date(master): Tue Nov 13 14:22:46 CET 2018 on sn-devel-144

(cherry picked from commit bb93e691ca9b1922bf552363a1e7d70792749d67)

Autobuild-User(v4-8-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-8-test): Fri Nov 23 13:52:04 CET 2018 on sn-devel-144