Fix netrotctl.c to flush network/serial before every transaction

https://github.com/Hamlib/Hamlib/issues/259

dummy/netrotctl.c

@@ -32,6 +32,8 @@
 #include "hamlib/rotator.h"
 #include "iofunc.h"
 #include "misc.h"
+#include "network.h"
+#include "serial.h"
 
 #include "rot_dummy.h"
 
@@ -45,6 +47,17 @@ static int netrotctl_transaction(ROT *rot, char *cmd, int len, char *buf)
 {
     int ret;
 
+    /* flush anything in the read buffer before command is sent */
+    if (rot->state.rotport.type.rig == RIG_PORT_NETWORK
+            || rot->state.rotport.type.rig == RIG_PORT_UDP_NETWORK)
+    {
+        network_flush(&rot->state.rotport);
+    }
+    else
+    {
+        serial_flush(&rot->state.rotport);
+    }
+
     ret = write_block(&rot->state.rotport, cmd, len);
 
     if (ret != RIG_OK)