Filter out ZeroTier packets that do not come from an expected source

Source/dvlnet/base_protocol.h

@@ -288,6 +288,9 @@ void base_protocol<P>::recv_ingame(packet &pkt, endpoint sender)
 		// normal packets
 		LogDebug("Invalid packet: packet source ({}) >= MAX_PLRS", pkt.Source());
 		return;
+	} else if (sender != peers[pkt.Source()]) {
+		LogDebug("Invalid packet: packet source ({}) received from unrecognized endpoint", pkt.Source());
+		return;
 	}
 	connected_table[pkt.Source()] = true;
 	peers[pkt.Source()] = sender;