Avoid turning off wifi tethering on interface down

The hostapd daemon can bring down an interface, followed by immediately bringing it up
and this results in us turning off tethering completely.

Wait for the right notification to enter tethered state after brining up hostapd.

Bug: 5135245
Change-Id: I95c8c0c4c2c99c03fce2d18c014eaff37ed4e762
diff --git a/wifi/java/android/net/wifi/WifiStateMachine.java b/wifi/java/android/net/wifi/WifiStateMachine.java
index 331d5c0..70d2c03 100644
--- a/wifi/java/android/net/wifi/WifiStateMachine.java
+++ b/wifi/java/android/net/wifi/WifiStateMachine.java
@@ -1087,13 +1087,11 @@
                         }
                     } catch (Exception e) {
                         Log.e(TAG, "Error configuring interface " + intf + ", :" + e);
-                        setWifiApEnabled(null, false);
                         return false;
                     }
 
                     if(mCm.tether(intf) != ConnectivityManager.TETHER_ERROR_NO_ERROR) {
                         Log.e(TAG, "Error tethering on " + intf);
-                        setWifiApEnabled(null, false);
                         return false;
                     }
                     return true;