af_packet use packet fanout, set flag: PACKET_FANOUT_FLAG_DEFRAG, if set,
causes packets to be defragmented before fanout is applied, the packets that
read from AF_PACKET socket maybe larger than the frame size and the mbuf size,
so the packet will be truncated.

In PACKET_FANOUT mode, each matching packet is enqueued onto only one socket in
the group. But when af_packet use one rx queue, there is no need to set packet
fanout.