packetpool: return one packet as well on sync now

If a thread is hitting the packet pool return on a 'sync_now' return
the packet also if it is the first packet since the last flush.

Bug: #6435.

src/tmqh-packetpool.c

@@ -172,6 +172,7 @@ void PacketPoolReturnPacket(Packet *p)
         my_pool->head = p;
     } else {
         PktPool *pending_pool = my_pool->pending_pool;
+        if (pending_pool == NULL || pending_pool == pool) {
             if (pending_pool == NULL) {
                 /* No pending packet, so store the current packet. */
                 p->next = NULL;
@@ -184,6 +185,8 @@ void PacketPoolReturnPacket(Packet *p)
                 p->next = my_pool->pending_head;
                 my_pool->pending_head = p;
                 my_pool->pending_count++;
+            }
+
             if (SC_ATOMIC_GET(pool->return_stack.sync_now) || my_pool->pending_count > max_pending_return_packets) {
                 /* Return the entire list of pending packets. */
                 SCMutexLock(&pool->return_stack.mutex);