T6456: Convert "monitor traffic" to modern op-mode wrapper

The old "monitor traffic" definition had misaligned arguments under the verbose node
and manually offered the same parameter keyword in multiple positions to emulate
flexible parameters.

I've wrapped tcpdump for op-mode and replicated the "varargs" style from mtr.py/mtr.xml.in
to present a few more parameters in a more flexible manner.

Changes to the Makefile were required for recursive varargs lookup.