mptcpd for Debian

There are comments for each specific rule in debian/rules.

The project is providing a few different binaries:

- a daemon: mptcpd in usr/libexec because a systemd service starts it

- a lib to help building plugins: libmptcpd

- some plugins for mptcpd: .so in usr/lib/*/mptcpd

- a lib to be used with LD_PRELOAD to create MPTCP sockets instead of TCP ones:
  libmptcpwrap in usr/lib/*/mptcpize

- a tool to force apps using MPTCP sockets with libmptcpwrap: mptcpize

Some Lintian warnings/errors have been ignored, see comments in
*.lintian-overrides files.

The build is currently not passing the "reproducible" test because of a bug with
doxygen 1.9.1. This will be fixed when switching to 1.9.3 version or later:
https://github.com/doxygen/doxygen/issues/8396

 -- Matthieu Baerts <matthieu.baerts@tessares.net>  Wed, 19 Jan 2022 16:31:56 +0100
