cmdmon: add serverstats command

Add a new command to obtain a server report with the new clientlog
statistics.

reports.h

@@ -99,6 +99,14 @@ typedef struct {
   uint32_t last_cmd_hit_ago;
 } RPT_ClientAccessByIndex_Report;
 
+typedef struct {
+  uint32_t ntp_hits;
+  uint32_t cmd_hits;
+  uint32_t ntp_drops;
+  uint32_t cmd_drops;
+  uint32_t log_drops;
+} RPT_ServerStatsReport;
+
 typedef struct {
   struct timeval when;
   double slewed_offset;