[IPv6] Revert "Allow buffer length to be greater than IP packet in IPv6"

[ActoryOu]

[IPv6] Revert PR#927 "Allow buffer length to be greater than IP packet in IPv6"

Description

Revert #927 because we're failing one critical test case in protocol tester.

Test Steps

Run test case IPv6/Datagram/009

Checklist:

• I have tested my changes. No regression in existing tests.
• I have modified and/or added unit-tests to cover the code changes in this Pull Request.

Related Issue

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[htibosch]

The packet length in IPv6 seems to be more critical than in IPv4, I didn't know that.
Note that we'll have to change the reception in the SAM driver: subtract 2 bytes from the received length.

[ActoryOu]

The packet length in IPv6 seems to be more critical than in IPv4, I didn't know that. Note that we'll have to change the reception in the SAM driver: subtract 2 bytes from the received length.

It's good to see your comment here.
Yeah it's better to handle this kind of "extra length" in network interface itself.

[shubnil]

The check for packet payload greater than the header length is specific to a particular SKU of SAM board. Hence, the decision to revert this change, so that the particular Network Interface can take the necessary active and pass the buffer to the FreeRTOS-plus-TCP stack in the standard form where the payload size matches with the header payload length.

[shubnil]

The packet length in IPv6 seems to be more critical than in IPv4, I didn't know that. Note that we'll have to change the reception in the SAM driver: subtract 2 bytes from the received length.

Do we know why we have those 2 extra bytes and if we will ever need them in the stack for any future processing.

[htibosch]

The patch #950 should correct the number of bytes received.