selftests: net: Add tests for failover of team-aggregated ports

selftests: net: Add tests for failover of team-aggregated ports

There are currently no kernel tests that verify the effect of setting
the enabled team driver option. In a followup patch, there will be
changes to this option, so it will be important to make sure it still
behaves as it does now.

The test verifies that tcp continues to work across two different team
devices in separate network namespaces, even when member links are
manually disabled.

Signed-off-by: Marc Harvey <marcharvey@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260409-teaming-driver-internal-v7-4-f47e7589685d@google.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>