Add maxchange directive

This directive sets the maximum allowed offset corrected on a clock
update.  The check is performed only after the specified number of
updates to allow a large initial adjustment of the system clock.  When
an offset larger than the specified maximum occurs, it will be ignored
for the specified number of times and then chronyd will give up
and exit (a negative value can be used to never exit).  In both cases
a message is sent to syslog.

chrony.texi

@@ -1192,6 +1192,7 @@ directives can occur in any order in the file.
 * logdir directive::            Specify directory for logging
 * mailonchange directive::      Send email if a clock correction above a threshold occurs
 * makestep directive::          Step system clock if large correction is needed
+* maxchange directive::         Set maximum allowed offset
 * manual directive::            Allow manual entry using chronyc's settime cmd.
 * maxclockerror directive::     Set maximum frequency error of local clock
 * maxupdateskew directive::     Stop bad estimates upsetting machine clock
@@ -2244,6 +2245,27 @@ makestep 1000 10
 This would step system clock if the adjustment is larger than 1000
 seconds, but only in the first ten clock updates.
 @c }}}
+@c {{{ maxchange
+@node maxchange directive
+@subsection maxchange
+This directive sets the maximum allowed offset corrected on a clock
+update.  The check is performed only after the specified number of
+updates to allow a large initial adjustment of the system clock.  When
+an offset larger than the specified maximum occurs, it will be ignored
+for the specified number of times and then @code{chronyd} will give up
+and exit (a negative value can be used to never exit).  In both cases
+a message is sent to syslog.
+
+An example of the use of this directive is
+
+@example
+maxchange 1000 1 2
+@end example
+
+After the first clock update, @code{chronyd} will check the offset on
+every clock update, it will ignore two adjustments larger than 1000
+seconds and exit on another one.
+@c }}}
 @c {{{ manual
 @node manual directive
 @subsection manual