net/vpp: Fix build

[jrm]

Summary

The build was failing because the cmake_install.cmake step for
vpp-api/python was calling pip install to download and install packages
from from PyPi.

Fix the build by:

• Add missing build dependencies
• patching src/vpp-api/python/CMakeLists.txt to use installed packages rather than downloading new ones.

[jrm]

Install the libraries with COPYTREE_SHARE

[thj]

Thanks, I've updated the other review.

This is able to make packets go with netmap which is a reasonable minimal test.

[jrm]

This was meant to be a temporary review to share ideas with @thj. Closing.