The implementation of scanning /proc files to do automatic port forwarding
is a bit awkwardly split between procfs_scan_listen() in util.c,
get_bound_ports() and related functions in conf.c and the initial setup
code in conf().

Consolidate all of this into port_fwd.h, which already has some related
definitions, and a new port_fwd.c.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

In practical terms, passt doesn't benefit from the additional
protection offered by the AGPL over the GPL, because it's not
suitable to be executed over a computer network.

Further, restricting the distribution under the version 3 of the GPL
wouldn't provide any practical advantage either, as long as the passt
codebase is concerned, and might cause unnecessary compatibility
dilemmas.

Change licensing terms to the GNU General Public License Version 2,
or any later version, with written permission from all current and
past contributors, namely: myself, David Gibson, Laine Stump, Andrea
Bolognani, Paul Holzinger, Richard W.M. Jones, Chris Kuhn, Florian
Weimer, Giuseppe Scrivano, Stefan Hajnoczi, and Vasiliy Ulyanov.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

...at the moment, just for consistency with packet.h, icmp.h,
tcp.h and udp.h.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

SPDX tags don't replace license files. Some notices were missing and
some tags were not according to the SPDX specification, too.

Now reuse --lint from the REUSE tool (https://reuse.software/) passes.

Reported-by: Martin Hauke <mardnh@gmx.de>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Detecting bound ports at start-up time isn't terribly useful: do this
periodically instead, if configured.

This is only implemented for TCP at the moment, UDP is somewhat more
complicated: leave a TODO there.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>