Introduce xfrm_interface tests

[rlmenge]

Introduce xfrm_interface tests. This is to validate the config option CONFIG_XFRM_INTERFACE
Steps:
1. Check if CONFIG_XFRM_INTERFACE is enabled in kernel config. (will skip if not)
2. Load the xfrm_interface module if not already loaded.
3. Verify the module is loaded successfully.
4. Create a test xfrm interface (xfrm0).
ip link add xfrm0 type xfrm dev eth0 if_id 100
5. Verify the interface was created.
ip link show
6. Clean up the test interface.
sudo ip link del xfrm0

[Copilot]

Pull request overview

This PR introduces comprehensive test coverage for the xfrm_interface kernel module, which is used for IPsec VPN tunnels. The tests validate that the CONFIG_XFRM_INTERFACE kernel configuration option is properly enabled and functional on Azure Linux VMs.

Key Changes:

• New test suite for XFRM interface functionality with two test cases
• Validates kernel module loading, interface creation, and module load/unload operations
• Includes proper cleanup and error handling for test isolation