[ns] change the node target

[chunlei liu <cliu@cis.ohio-state.edu>]

Hi,

I now have a simple question on ns. The question comes because I want to
insert a object between a node and a link. I want to find out which
component in a node has the link head as a target, change that target to
my object, and set my object's object to the link head.

But when I read the code for simplex-link in ns-lib.tcl and other code in
ns-link.tcl, ns-node.tcl, node.cc, etc, I could not find which component
set the target to the link head. If you happen to know the answer, can you
give me some help?

Thank you.

Chunlei