session manager support TCP fast open

src/session/session_manager.cpp

@@ -315,7 +315,8 @@ static void tcp_update(struct session_manager *mgr, struct session *sess, enum s
 
      if (unlikely(flags & TH_SYN))
      {
-          tcp_reassembly_set_recv_next(half->assembler, half->seq + 1);
+          // len > 0 is SYN with data (TCP Fast Open)
+          tcp_reassembly_set_recv_next(half->assembler, len ? half->seq : half->seq + 1);
      }
 
      seg = tcp_reassembly_expire(half->assembler, now);