Can't use Connected() in Disconnect since it just set disconnected.

Use p.connected directly. This restores the correct disconnection of peers when
we go over the limit. Found by dhill, fix by me.

peer.go

@@ -1065,7 +1065,7 @@ func (p *peer) Disconnect() {
 		return
 	}
 	close(p.quit)
-	if p.Connected() {
+	if atomic.LoadInt32(&p.connected) != 0 {
 		p.conn.Close()
 	}
 }