add ebpf() plugin and reuseport randomization

[bazsi]

ebpf() plugin and udp packet balancer: a new ebpf() plugin was added which
leverages the kernel's eBPF infrastructure to improve performance and
scalability of syslog-ng. The first ebpf based solution improves
performance when a single (or very few) senders generate most of the inbound
UDP traffic that syslog-ng needs to process. Normally, the kernel
distributes load between so-reuseport sockets by keeping each flow (e.g.
same source/dest ip/port) in its dedicated receiver. This fails to balance
the sockets properly if only a few senders are responsible for most of the
load. ebpf(reuseport()) will replace the original kernel algorithm with an
alternative that changes the algorithm, so individual packets will be
assigned to one of the sockets randomly, thereby producing a more uniform
load.

Example:

source s_udp {
        udp(so-reuseport(yes) port(2000) persist-name("udp1")
                ebpf(reuseport(sockets(4)))
        );
        udp(so-reuseport(yes) port(2000) persist-name("udp2"));
        udp(so-reuseport(yes) port(2000) persist-name("udp3"));
        udp(so-reuseport(yes) port(2000) persist-name("udp4"));
};

Depends on #4373

[kira-syslogng]

Build FAILURE

[kira-syslogng]

Build FAILURE

[kira-syslogng]

Build FAILURE

[kira-syslogng]

Build FAILURE

[bazsi]

This PR depends on some packages that we need to install into our tarball container, but the CI is run on a previous version. At the moment, I've added the installation of these packages in our actions workflow in a temporary commit. As soon as we are ready with the review, we should probably merge the dbld pieces first, wait for images to be generated and then merge the rest, while dropping the temporary change in the actions script.

[alltilla]

I have found some build/configure related things.

Some of them were not trivial for me to understand and recommend a fix, so I have fixed them on my working branch and opened a PR for your convenience: bazsi#17

Could you kindly check it out? Thanks!

[alltilla]

The dbld image dep PR went in, we can now rebase this to master and drop the workaround commit.

[alltilla]

Only one comment, otherwise LGTM.

[czanik]

Could you add some developer notes to the NEWS about the configure options and necessary dependencies?

[bazsi]

I've added a paragraph to the NEWS file. in short don't compile it, unless you need it. Also, it will be a nightmare to enable this in all distros.