MonoTorrent ignores tracker-supplied announce intervals

[lostmsu]

Repro

1. Setup a TrackerServer with low AnnounceInterval and MinAnnounceInterval
2. Connect to it using MonoTorrent client
3. Watch MonoTorrent only submitting announces every 30 minutes instead of using AnnounceInterval.

Notes

Happens because Tracker never updates LastAnnounceResponse from its default value of Unknown. But it uses that property to calculate intervals, see corresponding properties.

I think this line should be changed to

LastResponse = LastAnnounceResponse = response;

[lostmsu]

@alanmcgovern lol, GitHub closed the issue even though I only pushed the fix into my fork.