log - Convert LOG_FMT_* into an enum

LogTimeFormat is gaining options that are not timestamp formats. Group
the timestamp formats into an enum so that the rest of log_fmt can be
given to those options.

The values themselves are unchanged, so nothing is packed differently.

slurm/slurm.h

diff --git a/slurm/slurm.h b/slurm/slurm.h
index 0d8f364..4b09003 100644
--- a/slurm/slurm.h
+++ b/slurm/slurm.h
@@ -3018,15 +3018,19 @@
 #define CONF_FLAG_DISABLE_HTTP	SLURM_BIT(17) /* CommunicationParameters=disable_http */
 #define CONF_FLAG_HC_REPORT_HEALTH SLURM_BIT(18) /* SlurmctldParameters=health_check_report */
 
-#define LOG_FMT_ISO8601_MS      0
-#define LOG_FMT_ISO8601         1
-#define LOG_FMT_RFC5424_MS      2
-#define LOG_FMT_RFC5424         3
-#define LOG_FMT_CLOCK           4
-#define LOG_FMT_SHORT           5
-#define LOG_FMT_THREAD_ID       6
-#define LOG_FMT_RFC3339         7
-#define LOG_FMT_OMIT 8
+/* Timestamp format for LogTimeFormat. */
+typedef enum {
+	LOG_FMT_ISO8601_MS = 0,
+	LOG_FMT_ISO8601 = 1,
+	LOG_FMT_RFC5424_MS = 2,
+	LOG_FMT_RFC5424 = 3,
+	LOG_FMT_CLOCK = 4,
+	LOG_FMT_SHORT = 5,
+	LOG_FMT_THREAD_ID = 6,
+	LOG_FMT_RFC3339 = 7,
+	LOG_FMT_OMIT = 8,
+} log_fmt_t;
+
 /* Default timestamp format */
 #define LOG_FMT_DEFAULT LOG_FMT_ISO8601_MS