local: add new driver call to set synchronization status

This will be used to set the kernel adjtimex() variables to allow other
applications running on the system to know if the system clock is
synchronized and the estimated error and the maximum error.

sys_netbsd.c

@@ -307,7 +307,8 @@ SYS_NetBSD_Initialise(void)
   lcl_RegisterSystemDrivers(read_frequency, set_frequency, 
                             accrue_offset, apply_step_offset,
                             get_offset_correction,
-                            NULL /* set_leap */);
+                            NULL /* set_leap */,
+                            NULL /* set_sync_status */);
 
 }