build: Make the build work on Debian 11

build: Make the build work on Debian 11

Debian 11 has some packages that have changed, and need adjustment.
Also - its default compiler is gcc 10, which, contrary to either gcc 8
or gcc 11 prints a bunch of warnings, which fails compilation.
And there is no gcc 11 package.

Therefore, use clang for this build.

Additionally, python 3.9 has exposed this issue:
https://bugs.python.org/issue42580

Therefore, make a local patch to scapy to tackle it.

Type: feature
Signed-off-by: Andrew Yourtchenko <ayourtch@gmail.com>
Change-Id: I7b9c0f852ab97fe3c1feca3f22020ac0970ba3e2