MINOR: stats: use tv_remain() to precisely compute the uptime

We'll have to support reporting sub-second uptimes, so let's use the
appropriate function which will automatically adjust the tv_usec field.
In addition to this, it will also report a more accurate uptime thanks
to considering the sub-second part in the result.
diff --git a/src/stats.c b/src/stats.c
index a352a9b..4b58f66 100644
--- a/src/stats.c
+++ b/src/stats.c
@@ -4293,7 +4293,7 @@
  */
 int stats_fill_info(struct field *info, int len, uint flags)
 {
-	unsigned int up = (now.tv_sec - start_date.tv_sec);
+	struct timeval up;
 	struct buffer *out = get_trash_chunk();
 
 #ifdef USE_OPENSSL
@@ -4307,6 +4307,8 @@
 	}
 #endif
 
+	tv_remain(&start_date, &now, &up);
+
 	if (len < INF_TOTAL_FIELDS)
 		return 0;
 
@@ -4324,9 +4326,9 @@
 	info[INF_PID]                            = mkf_u32(FO_STATUS, pid);
 
 	info[INF_UPTIME]                         = mkf_str(FN_DURATION, chunk_newstr(out));
-	chunk_appendf(out, "%ud %uh%02um%02us", up / 86400, (up % 86400) / 3600, (up % 3600) / 60, (up % 60));
+	chunk_appendf(out, "%ud %uh%02um%02us", (uint)up.tv_sec / 86400, ((uint)up.tv_sec % 86400) / 3600, ((uint)up.tv_sec % 3600) / 60, ((uint)up.tv_sec % 60));
 
-	info[INF_UPTIME_SEC]                     = mkf_u32(FN_DURATION, up);
+	info[INF_UPTIME_SEC]                     = mkf_u32(FN_DURATION, up.tv_sec);
 	info[INF_START_TIME_SEC]                 = mkf_u32(FN_DURATION, start_date.tv_sec);
 	info[INF_MEMMAX_MB]                      = mkf_u32(FO_CONFIG|FN_LIMIT, global.rlimit_memmax);
 	info[INF_MEMMAX_BYTES]                   = mkf_u32(FO_CONFIG|FN_LIMIT, global.rlimit_memmax * 1048576L);