This commit adds pybind11 glue code for the userland chdr parsing code
introduced in the uhd::utils::chdr namespace. Additionally, it moves
some pybind11 adapter code to a common pybind_adaptors.hpp file which
originally existed in the cal_python.hpp file.
This commit also adds unit tests for the python bindings using a
captured wireshark trace which is located in rfnoc_packets_*.py and some
handwritten packets in hardcoded_packets.py
Signed-off-by: Samuel O'Brien <sam.obrien@ni.com>
