[ns] question about struct if_head

["Cheng Li" <licheng@sjtu.edu.cn>]

hi:

The "class Channel" (in channel.h) has a member declared as below:

class Channel {
...
public:
	struct if_head	ifhead_
...
}

It is strange that I can not find the actual definition of the "struct 
if_hend" even though I have greped all the files in the ~/ns directory. 
Could anyone give me some explain?

danaus