Add support for TCX expected_revision

[anfredette]

The kernel's TCX support includes the option to specify an expected_revision on attach calls. The expected_revision is compared to the current revision on the attach point by the kernel, which will fail the operation if they don't match. This allows the user to ensure that nothing has changed between the time the state of the attach point was checked and when the attach is being performed if needed.

In order to use this feature effectively, there needs to be a way for the user to get the current state of a TCX attach point which doesn't currently exist in Aya.

expected_revision support was omitted from the initial implementation in pr #921 until it can be fully implemented.

This feature should include the following components:

• An API to retrieve the state of TCX on a given attach point (i.e., interface + direction) based on the BPF_PROG_QUERY syscall. This API should return at least the current revision and the list of existing TCX programs attached with their position in the chain.
• Support for expected_revision in the TCX attach code.
• Extend the TCX integration tests with some expected_revision examples.
• Use the new API to also validate that the programs in the integration test are attached in the expected order.