Fix Close connection for invalid header

RemoteAddr() must close the connection and clear the buffer if we
receive a invalid PROXY protocol header.

Change the client test as it can get an EOF or a ECONNRESET.

protocol.go

@@ -110,6 +110,8 @@ func (p *Conn) RemoteAddr() net.Addr {
 	p.once.Do(func() {
 		if err := p.checkPrefix(); err != nil && err != io.EOF {
 			log.Printf("[ERR] Failed to read proxy prefix: %v", err)
+			p.Close()
+			p.bufReader = bufio.NewReader(p.conn)
 		}
 	})
 	if p.srcAddr != nil {