What is the role of steganography in network security?
I’m not aware of any uses of steganography in network applications, and considering almost all of the networking protocols are open protocols, there’s little room for the application of it. If you need security, you use various forms of encryption.

That being said, the only example I can think of of steganography in modern days is, some printers also printing out some form of a serial code and timestamp in a (almost) hidden part of the printed out material.