$q marker_class 1|2|3|4
For a deterministic marker, selects which class packets should be marked with.
$q marker_frc f1 f2 f3 f4
For a statistical marker, gives the fraction of packets that should be marked
from each class. For instance, using 0.1 for f1 means that 10 percent of the
traffic coming to the Marker link will be marked as Class 1.