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.

candm.h

@@ -88,7 +88,8 @@
 #define REQ_MODIFY_MAXDELAYDEVRATIO 47
 #define REQ_RESELECT 48
 #define REQ_RESELECTDISTANCE 49
-#define N_REQUEST_TYPES 50
+#define REQ_MODIFY_MAKESTEP 50
+#define N_REQUEST_TYPES 51
 
 /* Special utoken value used to log on with first exchange being the
    password.  (This time value has long since gone by) */
@@ -187,6 +188,12 @@ typedef struct {
   int32_t EOR;
 } REQ_Modify_Maxupdateskew;
 
+typedef struct {
+  int32_t limit;
+  Float threshold;
+  int32_t EOR;
+} REQ_Modify_Makestep;
+
 typedef struct {
   Timeval ts;
   int32_t EOR;
@@ -362,7 +369,8 @@ typedef struct {
    subnets accessed and client accesses
 
    Version 6 : added padding to requests to prevent amplification attack,
-   changed maximum number of samples in manual list to 16
+   changed maximum number of samples in manual list to 16, new commands: modify
+   makestep
  */
 
 #define PROTO_VERSION_NUMBER 6
@@ -407,6 +415,7 @@ typedef struct {
     REQ_Modify_Minstratum modify_minstratum;
     REQ_Modify_Polltarget modify_polltarget;
     REQ_Modify_Maxupdateskew modify_maxupdateskew;
+    REQ_Modify_Makestep modify_makestep;
     REQ_Logon logon;
     REQ_Settime settime;
     REQ_Local local;