network: unset Link.ndisc_configured only when a new address or route is requested
    
    This fixes an issue introduced by af2aea8bb64b0dc42ecbe5549216eb567681a803.
    
    When an outdated address or route is passed to link_request_address()/route(),
    then they return 0 and the address or route will not be assigned. Such
    situation can happen when we receive RA with zero lifetime. In that
    case, we should not unset Link.ndisc_configured flag, otherwise even
    no new address nor route will assigned, the interface will enter to the
    configuring state, and unnecessary DBus property change is emit and the state
    file will be updated. That makes resolved or timesyncd triggered to
    reconfigure the interface.
    
    Fixes #25456.
    
    (cherry picked from commit d9a95033bf3a2a8cb886847dd7404a53336ac090)