Remove STRUIO_IP support from ip_cksum.c
Review Request #2402 — Created Oct. 17, 2019 and updated — Latest diff uploaded
This removes support for the unused STRUIO_IP flag and vastly simplifies the ip_cksum.c source
A test mockup using the old and new ip_cksum code was created (attached to the ticket) and the result ran with a rather contrived mblk_t chain (odd lengths, 0 length mblk_ts, unaligned data, etc.) and the new code produced the same checksum in all cases.