This class is the only TclObject in the network dynamics code.
The shadow class is called DynaLink../ns-2/dynalink.h.
The class supports one bound variable, status_.
status_ is 1 when the link is up, and 0 when the link is down.
The shadow object's recv../ns-2/dynalink.ccDynaLink::recv
method checks the status_ variable, to decide whether or not
a packet should be forwarded.