wifi: Make EMLSR link switch test more robust

Wait for one additional TimeStep before checking which link the main
PHY is switching to. We were waiting for a PHY slot to account for
backoff slot alignment, but this is not sufficient when channel access
is delayed by a whole PHY slot because the check is performed before
channel access is granted and the main PHY starts switching.

src/wifi/test/wifi-emlsr-link-switch-test.cc

@@ -1677,7 +1677,9 @@ EmlsrSwitchMainPhyBackTest::MainPhySwitchInfoCallback(std::size_t index,
             m_staMacs[0]->GetDevice()->GetNode()->AddApplication(
                 GetApplication(UPLINK, 0, 1, 500, 4));
             // channel access can be obtained within a slot due to slot alignment
-            Simulator::Schedule(m_apMac->GetWifiPhy(m_linkIdForTid4)->GetSlot(), [=, this]() {
+            Simulator::Schedule(
+                m_apMac->GetWifiPhy(m_linkIdForTid4)->GetSlot() + TimeStep(1),
+                [=, this]() {
                     auto advEmlsrMgr =
                         DynamicCast<AdvancedEmlsrManager>(m_staMacs[0]->GetEmlsrManager());
 
@@ -1687,7 +1689,7 @@ EmlsrSwitchMainPhyBackTest::MainPhySwitchInfoCallback(std::size_t index,
                     NS_TEST_EXPECT_MSG_EQ(
                         +advEmlsrMgr->m_mainPhySwitchInfo.to,
                         +(advEmlsrMgr->m_interruptSwitching ? m_linkIdForTid4 : m_mainPhyId),
-                    "Main PHY is switching to wrong link");
+                        "Test index " << +m_testIndex << ": Main PHY is switching to wrong link");
                 });
         });
         InsertEventsForQosTid4();