fix prepend ptr when sequence num. changes

[LennSar]

in case of multiple threads handling multiple packets it might happen that the sequence number of a paket changes before it got send out. In that case the checksum for that packet needs to be recalculated and the new sequence number must be added to the tcp header.
When this is done, the size of the TCP Header will be removed from the available headspace and length twice for a packet which later on results in an assertion because the prepend_ptr will be smaller then the start_ptr.
This is fixed by adding the header size before hitting the continue statement of the for loop.

[fdesbiens]

Thank you for this contribution, @LennSar!

Before we can accept it, you need to sign the Eclipse Contributor Agreement (ECA). The purpose of the ECA is to provide a written record that you have agreed to provide your code and documentation contributions under the licenses used by the Eclipse ThreadX project. It also makes it clear that you are promising that what you are contributing to Eclipse is code you wrote, and you have the necessary rights to contribute it to our projects. And finally, it documents a commitment from you that your open source contributions will be permanently on the public record.

Signing the ECA requires an Eclipse Foundation account if you do not already have one. You can create one for free at https://accounts.eclipse.org.

Be sure to use the same email address when you register for the account that you intend to use on Git commit records. Also, please add your GitHub ID to your Eclipse account. This enables synchronisation between Eclipse-owned infrastructure and GitHub.

Here is the link to sign the ECA:
https://accounts.eclipse.org/user/login?destination=user/eca

[LennSar]

Thanks for the links! I signed the ECA and connected my Github account. I see the errors still. Hopefully that just takes some time to update? I'll check in tomorrow again.

[fdesbiens]

@LennSar Yes, synchronisation can take a few hours. I tried to force a rerun of the ECA check and it failed. I will try again tomorrow. That said, I can see your account and can confirm the ECA has been signed. Unless there are technical issues, everything should be all right tomorrow.

[fdesbiens]

Hi @LennSar.

The check passes now. I will find someone to review. Thanks again!

[LennSar]

perfect. Thanks for your help. These regression tests that are failing right now aren't because of my changes right? At least the error message doesn't seem to be caused by them?!

[fdesbiens]

Hi @LennSar.

We are having a bit of trouble with our GitHub actions recently. I need to investigate. In any case, part of the review process involves running the test suite manually just in case... So, don't worry for now.