igb: Fix constant media auto sense switching when no cable is connected
    
    At least on the i350 there is an annoying behavior that is maybe also
    present on 82580 devices, but was probably not noticed yet as MAS is not
    widely used.
    
    If no cable is connected on both fiber/copper ports the media auto sense
    code will constantly swap between them as part of the watchdog task and
    produce many unnecessary kernel log messages.
    
    The swap code responsible for this behavior (switching to fiber) should
    not be executed if the current media type is copper and there is no signal
    detected on the fiber port. In this case we can safely wait until the
    AUTOSENSE_EN bit is cleared.
    
    Signed-off-by: Manfred Rudigier <manfred.rudigier@omicronenergy.com>
    Tested-by: Aaron Brown <aaron.f.brown@intel.com>
    Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>