Improved receive.go

- Fixed configuration listen-port semantics
- Improved receive.go code for updating listen port
- Updated under load detection, how follows the kernel space implementation
- Fixed trie bug accidentally introduced in last commit
- Added interface name to log (format still subject to change)
- Can now configure the logging level using the LOG_LEVEL variable
- Begin porting netsh.sh tests
- A number of smaller changes

src/conn.go

@@ -0,0 +1,40 @@
+package main
+
+import (
+	"net"
+)
+
+func updateUDPConn(device *Device) error {
+	var err error
+	netc := &device.net
+	netc.mutex.Lock()
+
+	// close existing connection
+
+	if netc.conn != nil {
+		netc.conn.Close()
+	}
+
+	// open new connection
+
+	if device.tun.isUp.Get() {
+		conn, err := net.ListenUDP("udp", netc.addr)
+		if err == nil {
+			netc.conn = conn
+			signalSend(device.signal.newUDPConn)
+		}
+	}
+
+	netc.mutex.Unlock()
+	return err
+}
+
+func closeUDPConn(device *Device) {
+	netc := &device.net
+	netc.mutex.Lock()
+	if netc.conn != nil {
+		netc.conn.Close()
+	}
+	netc.mutex.Unlock()
+	signalSend(device.signal.newUDPConn)
+}