ntp: define NTP port for configuration code

conf.c

@@ -79,7 +79,7 @@ static void parse_tempcomp(char *);
 static int restarted = 0;
 static char *rtc_device;
 static int acquisition_port = -1;
-static int ntp_port = 123;
+static int ntp_port = NTP_PORT;
 static char *keys_file = NULL;
 static char *drift_file = NULL;
 static char *rtc_file = NULL;
@@ -1179,7 +1179,7 @@ parse_broadcast(char *line)
     }
   } else {
     /* default port */
-    port = 123;
+    port = NTP_PORT;
   }
 
   destination = (NTP_Broadcast_Destination *)ARR_GetNewElement(broadcasts);

ntp.h

@@ -38,6 +38,9 @@ typedef struct {
 
 typedef uint32_t NTP_int32;
 
+/* The UDP port number used by NTP */
+#define NTP_PORT 123
+
 /* The NTP protocol version that we support */
 #define NTP_VERSION 4