[Draft] Add announce_port support

[0xThiebaut]

Warning

Draft pending next release including arvidn/libtorrent#7771

The announce_port setting permits to overwrite the port passed along to trackers as the &port= parameter. If left as the default, the listening port is used. This setting is only meant for very special cases where a seed's listening port differs from the effectively exposed port (e.g., through external NAT-PMP). See arvidn/libtorrent#7771 for an example use-case.

This PR adds the relevant setting alongside the existing announce_ip setting.

The setting subsequently modifies the announced port (&port=1234):

127.0.0.1 - - [27/Oct/2024 09:44:16] "GET /announce?info_hash=%a7%801%f7%3b%a1k%3a%8e%b6%84%dd%cfyw%f1%f3%b8m!&peer_id=-qB5100-YwWihiQ4KGdM&port=1234&uploaded=0&downloaded=0&left=0&corrupt=0&key=CEDD0BC7&event=started&numwant=200&compact=1&no_peer_id=1&supportcrypto=1&redundant=0&ip=1.2.3.4 HTTP/1.1" 404 -

[Chocobo1]

You should guard against libtorrent version here and only here:

Suggested change

	// Port to announce to trackers
	settingsPack.set_int(lt::settings_pack::announce_port, announcePort());
	#if LIBTORRENT_VERSION_NUM >= XXXXX // please fill the correct version in
	// Port to announce to trackers
	settingsPack.set_int(lt::settings_pack::announce_port, announcePort());
	#endif

[0xThiebaut]

Thanks a lot for the review. I will resolve this item once the merged arvidn/libtorrent#7771 reaches a release.

[0xThiebaut]

On a side-note, the requires restart statement was copied over from the similar announce_ip setting; I'm however doubting whether this is an accurate statement for both.