* Simplified checksum calculation and verification
* Fixed tests
* UDP: using NewBoundedFrame to create a Frame instance limited to the actual frame size.
* Minor: renamed some functions
* Commented and made more readable consecutive SetCRC calls.
* Fixed icmp checksum calculation after rebase
* Replaced NewBoundedFrame with explicit validation
* Checksum 0x0000 is returned as 0xFFFF (mandatory for UDP, common for TCP)
* Both checksum zero values (0x0000 and 0xFFFF) are accepted when receiving
* Rename parameter in VerifySum16 to expectedSum16
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Co-authored-by: Pat Whittingslow <graded.sp@gmail.com>
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