networkBandwidthGenericChecks: Drop useless check
    
    There's a check right at the beginning of the function that
    shortcuts if the function was called over all NULL arguments.
    However, this was meant just as a fool-proof check so that we
    don't crash if function is used in a bad manner. Anyway, it makes
    Coverity unhappy as it then thinks any of the arguments could be
    NULL. Well, with the current state of the code it can't.
    
    Signed-off-by: Michal Privoznik <mprivozn@redhat.com>