Set maximum number of samples in manual list reply to 16

In chronyd the maximum number of manual samples is 16, so there is no
need to keep room for 32 samples in the command reply. This limits the
maximum assumed size of the reply packet.

candm.h

@@ -587,7 +587,7 @@ typedef struct {
   RPY_ClientAccesses_Client clients[MAX_CLIENT_ACCESSES];
 } RPY_ClientAccessesByIndex;
 
-#define MAX_MANUAL_LIST_SAMPLES 32
+#define MAX_MANUAL_LIST_SAMPLES 16
 
 typedef struct {
   Timeval when;