Add error reporting for Tethering.

Also make the usb interface configuration more robust so retries are possible.

Makes all Tethering errors recoverable - no harm letting them try again anyway.  Worst case
is they need to reboot.

services/java/com/android/server/ConnectivityService.java

@@ -1457,15 +1457,36 @@ public class ConnectivityService extends IConnectivityManager.Stub {
     }
 
     // javadoc from interface
-    public boolean tether(String iface) {
+    public int tether(String iface) {
         enforceTetherChangePermission();
-        return isTetheringSupported() && mTethering.tether(iface);
+
+        if (isTetheringSupported()) {
+            return mTethering.tether(iface);
+        } else {
+            return ConnectivityManager.TETHER_ERROR_UNSUPPORTED;
+        }
     }
 
     // javadoc from interface
-    public boolean untether(String iface) {
+    public int untether(String iface) {
         enforceTetherChangePermission();
-        return isTetheringSupported() && mTethering.untether(iface);
+
+        if (isTetheringSupported()) {
+            return mTethering.untether(iface);
+        } else {
+            return ConnectivityManager.TETHER_ERROR_UNSUPPORTED;
+        }
+    }
+
+    // javadoc from interface
+    public int getLastTetherError(String iface) {
+        enforceTetherAccessPermission();
+
+        if (isTetheringSupported()) {
+            return mTethering.getLastTetherError(iface);
+        } else {
+            return ConnectivityManager.TETHER_ERROR_UNSUPPORTED;
+        }
     }
 
     // TODO - proper iface API for selection by property, inspection, etc
@@ -1499,6 +1520,11 @@ public class ConnectivityService extends IConnectivityManager.Stub {
         return mTethering.getTetheredIfaces();
     }
 
+    public String[] getTetheringErroredIfaces() {
+        enforceTetherAccessPermission();
+        return mTethering.getErroredIfaces();
+    }
+
     // if ro.tether.denied = true we default to no tethering
     // gservices could set the secure setting to 1 though to enable it on a build where it
     // had previously been turned off.