Check if parameters set right for ipfwd/test_dip_sip.py

[ljyfree]

Description

Steps to reproduce the issue:
1.set up t1 topology
2.make sure DUT had set up ipv4/ipv6 neighbor with 32 EOS VMs
3.run ipfwd/test_dip_sip.py

def run_test_ipv4(ptfadapter, gather_facts):
    logger.info("Running test with ipv4 packets")
    dst_host_ipv4 = str(ip_address(unicode(gather_facts['dst_router_ipv4'])) + 1)
    pkt = testutils.simple_udp_packet(
        eth_dst=gather_facts['src_router_mac'],
        eth_src=gather_facts['src_host_mac'],
        ip_src=dst_host_ipv4,
        ip_dst=dst_host_ipv4,
        ip_ttl=DEFAULT_HLIM_TTL
    )
    logger.info("\nSend Packet:\neth_dst: {}, eth_src: {}, ipv6 ip: {}".format(
        gather_facts['src_router_mac'], gather_facts['src_host_mac'], dst_host_ipv4)
    )

    testutils.send(ptfadapter, int(gather_facts['src_port_ids'][0]), pkt)

    pkt = testutils.simple_udp_packet(
        eth_dst=gather_facts['dst_host_mac'],
        eth_src=gather_facts['dst_router_mac'],
        ip_src=dst_host_ipv4,
        ip_dst=dst_host_ipv4,
        ip_ttl=DEFAULT_HLIM_TTL-1
    )

I notice both of ingress pkt 's src_ip and dst_ip are set as dst_host_ipv4, was it designed on purpose?
It should trigger DUT send ICMP Redirect pkt with ingress pkt as its payload , whose length would increase.
So why expect egress pkt with the same length as ingress one?