set ASYNC_LOW_LATENCY flag on serial device just like setserial does to fix huge latency found on recent kernel versions

src/lib/ebus/device.cpp

@@ -27,6 +27,9 @@
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <netinet/tcp.h>
+#ifdef HAVE_LINUX_SERIAL
+#  include <linux/serial.h>
+#endif
 #include <errno.h>
 #ifdef HAVE_PPOLL
 #  include <poll.h>
@@ -190,6 +193,14 @@ result_t SerialDevice::open() {
     return RESULT_ERR_DEVICE;
   }
 
+#ifdef HAVE_LINUX_SERIAL
+  struct serial_struct serial;
+  if (ioctl(m_fd, TIOCGSERIAL, &serial) == 0) {
+    serial.flags |= ASYNC_LOW_LATENCY;
+    ioctl(m_fd, TIOCSSERIAL, &serial);
+  }
+#endif
+
   // save current settings
   tcgetattr(m_fd, &m_oldSettings);