test(client): avoid scheduler-dependent timing assertions

crates/irtt-client/tests/linux_transport.rs

@@ -108,8 +108,11 @@ fn assert_kernel_send_endpoint(event: &ClientEvent, before_send: SystemTime) {
     let selected =
         i128::from(timing.receive_wall_ns.unwrap()) - one_way.client_to_server.unwrap().as_nanos();
     assert!(selected >= ns(before_send));
-    assert!(
-        selected < ns(sent_at.wall),
+    // TX_SOFTWARE may arrive before or after send returns; only equality
+    // identifies the userspace fallback. Receipt remains the upper bound.
+    assert_ne!(
+        selected,
+        ns(sent_at.wall),
         "TX timestamp was not observed; userspace fallback is insufficient"
     );
     assert!(selected <= ns(received_at.wall));