client: add second form of makestep command

The second form configures the automatic stepping, similarly to the
makestep directive. It has two parameters, stepping threshold (in
seconds) and number of future clock updates for which will be the
threshold active. This can be used with the burst command to quickly
make a new measurement and correct the clock by stepping if needed,
without waiting for chronyd to complete the measurement and update the
clock.

cmdmon.c

@@ -160,7 +160,8 @@ static const char permissions[] = {
   PERMIT_AUTH, /* MODIFY_POLLTARGET */
   PERMIT_AUTH, /* MODIFY_MAXDELAYDEVRATIO */
   PERMIT_AUTH, /* RESELECT */
-  PERMIT_AUTH  /* RESELECTDISTANCE */
+  PERMIT_AUTH, /* RESELECTDISTANCE */
+  PERMIT_AUTH, /* MODIFY_MAKESTEP */
 };
 
 /* ================================================== */
@@ -908,6 +909,16 @@ handle_modify_maxupdateskew(CMD_Request *rx_message, CMD_Reply *tx_message)
 
 /* ================================================== */
 
+static void
+handle_modify_makestep(CMD_Request *rx_message, CMD_Reply *tx_message)
+{
+  REF_ModifyMakestep(ntohl(rx_message->data.modify_makestep.limit),
+                     UTI_FloatNetworkToHost(rx_message->data.modify_makestep.threshold));
+  tx_message->status = htons(STT_SUCCESS);
+}
+
+/* ================================================== */
+
 static void
 handle_settime(CMD_Request *rx_message, CMD_Reply *tx_message)
 {
@@ -1940,6 +1951,10 @@ read_from_cmd_socket(void *anything)
           handle_modify_maxupdateskew(&rx_message, &tx_message);
           break;
 
+        case REQ_MODIFY_MAKESTEP:
+          handle_modify_makestep(&rx_message, &tx_message);
+          break;
+
         case REQ_LOGON:
           /* If the log-on fails, record the reason why */
           if (!issue_token) {