AD: Initialize user_map_cnt in server mode
    
    user_map_cnt was initialized when all the traditional back ends are
    initialized. However, for the server mode, we simply copy the defaults
    and the count was left zeroed, which led to crashes.
    
    Down the road, we should consider tying the map and the attribute count
    together (see ticket #2336)
    
    Reviewed-by: Pavel Reichl <preichl@redhat.com>
    (cherry picked from commit 35d420c5d4609b6e999920e38a9b2ec40a0e1ac4)