Why I did it
This is to fix test_forward_ip_packet_with_0xffff_chksum_tolerant test failure on 720DT-48S. IP packets with checksum set to 0xffff will be forwarded with the same checksum on this platform, instead of updating to the correct value.
How I did it
Add bcm config sai_verify_incoming_chksum=0 so that checksum is updated instead of being left unchanged when checksum is 0xffff. Note that packets with invalid checksum are still dropped with this config.
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