flowworker: don't keep unnecessary flow reference

Flow stream/detect/log flush packets, don't hold on to the flow
beyond the flow worker module.

src/flow-worker.c

@@ -406,6 +406,9 @@ static inline void FlowWorkerStreamTCPUpdate(ThreadVars *tv, FlowWorkerThreadDat
                 x->flow, x->flowflags & FLOW_PKT_TOSERVER ? STREAM_TOSERVER : STREAM_TOCLIENT);
         FLOWWORKER_PROFILING_END(x, PROFILE_FLOWWORKER_TCPPRUNE);
 
+        /* no need to keep a flow ref beyond this point */
+        FlowDeReference(&x->flow);
+
         if (timeout) {
             PacketPoolReturnPacket(x);
         } else {