issue: 3574064 Allow tx segment split on ACK recv

[iftahl]

Description

This change will allow to piggyback the ACK when a TCP segment split is anticiapted due to small tx congestion window. We will not send empty ack, and instead split the next unsent segment to fit into the congestion window, and piggyback the ACK we need to send.

We hit a deadlock before this change where application sent data and didn't get completions by XLIO because the congestion window was still small (start of the world), and we didn't send any data on received ack by the remote side. Instead - we should send any data we got on unsent queue once we get any ACK by remote side.

Change type

What kind of change does this PR introduce?

• [x] Bugfix
• [ ] Feature
• [ ] Code style update
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] CI related changes
• [ ] Documentation content changes
• [ ] Tests
• [ ] Other

Check list

• [ ] Code follows the style de facto guidelines of this project
• [ ] Comments have been inserted in hard to understand places
• [ ] Documentation has been updated (if necessary)
• [ ] Test has been added (if possible)

[iftahl]

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[pasis]

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