flow/manager: improve doc; minor cleanup

Explain meaning of `ts` in flow managers main loop.

src/flow-manager.c

@@ -827,7 +827,6 @@ static TmEcode FlowManager(ThreadVars *th_v, void *thread_data)
     uint64_t sleep_per_wu = 0;
     bool prev_emerg = false;
     uint32_t other_last_sec = 0; /**< last sec stamp when defrag etc ran */
-    SCTime_t ts;
 
     /* don't start our activities until time is setup */
     while (!TimeModeIsReady()) {
@@ -850,8 +849,10 @@ static TmEcode FlowManager(ThreadVars *th_v, void *thread_data)
     while (run) {
         bool emerg = ((SC_ATOMIC_GET(flow_flags) & FLOW_EMERGENCY) != 0);
 
-        /* Get the time */
-        ts = TimeGet();
+        /* Get the time: real time in live mode, or a min() of the
+         * "active" threads in offline mode. See TmThreadsGetMinimalTimestamp */
+        SCTime_t ts = TimeGet();
+
         SCLogDebug("ts %" PRIdMAX "", (intmax_t)SCTIME_SECS(ts));
         uint64_t ts_ms = SCTIME_MSECS(ts);
         const bool emerge_p = (emerg && !prev_emerg);