Wifi CTS: Check for tethering support

Skip tethering test on devices that don't support tethering.

Bug: 175617731

Test: CtsWifiTestCases after 'settings put global tether_support 0'
Change-Id: I8f464de74caa1dcf4465a6597482b0354ba8b6fa
diff --git a/tests/tests/wifi/src/android/net/wifi/cts/WifiManagerTest.java b/tests/tests/wifi/src/android/net/wifi/cts/WifiManagerTest.java
index 8910902..44b2c92 100644
--- a/tests/tests/wifi/src/android/net/wifi/cts/WifiManagerTest.java
+++ b/tests/tests/wifi/src/android/net/wifi/cts/WifiManagerTest.java
@@ -1670,6 +1670,10 @@
         TestSoftApCallback callback = new TestSoftApCallback(mLock);
         try {
             uiAutomation.adoptShellPermissionIdentity();
+            // check that tethering is supported by the device
+            if (!mTetheringManager.isTetheringSupported()) {
+                return;
+            }
             turnOffWifiAndTetheredHotspotIfEnabled();
             verifyRegisterSoftApCallback(executor, callback);