Description

This PR attempts to solve the deadlock produced when a read operation never completes (e.g. peer blocks before ending a transmission), and the TCP channel resource is disconnected (normally on closure while cleaning the associated transport).
Summing up, the solution consists in shutting down the socket before acquiring the culprit read mutex, so that any ongoing write/read operations are aborted even if not completed.

In addition, some other changes in this PR target general thread safety and attempt to improve overall resilience:

• New "disconnecting" state to protect from concurrent connect/disconnects.
• Assert that socket options are only configured before connection is established.

@Mergifyio backport 3.3.x 3.2.x 2.14.x

Contributor Checklist

• Commit messages follow the project guidelines.

• The code follows the style guidelines of this project.

• Tests that thoroughly check the new feature have been added/Regression tests checking the bug and its fix have been added; the added tests pass locally

• N/a Any new/modified methods have been properly documented using Doxygen.

• N/a Any new configuration API has an equivalent XML API (with the corresponding XSD extension)

• Changes are backport compatible: they do NOT break ABI nor change library core behavior.

• Changes are API compatible.

• N/a New feature has been added to the versions.md file (if applicable).

• N/a New feature has been documented/Current behavior is correctly described in the documentation.

• Applicable backports have been included in the description.

Reviewer Checklist

• The PR has a milestone assigned.
• The title and description correctly express the PR's purpose.
• Check contributor checklist is correct.
• N/a If this is a critical bug fix, backports to the critical-only supported branches have been requested.
• Check CI results: changes do not issue any warning.
• Check CI results: failing tests are unrelated with the changes.