CVE-2015-5370: s4:librpc/rpc: avoid using hs->p->conn->security_state.auth_info in dcerpc_bh_auth_info()

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11344

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Günther Deschner <gd@samba.org>
