IFP: do not create client socket
    
    There is no need for client socket in IFP responder,
    since it uses D-Bus for communication with clients.
    
    Resolves:
    https://fedorahosted.org/sssd/ticket/2290
    
    Reviewed-by: Pavel Březina <pbrezina@redhat.com>
    (cherry picked from commit 0a6fa194bad18f417dc8542d3b8f654f898375c5)