Fix: ConnectivityManager is initialized with a wrong context

ActivityThread#setHttpProxy uses a system context to get
a ConnectivityManager instance. If it's not already cached, the
system service registry will cache this instance initialized
with the system context, and subsequent calls to get this service
will return the bad instance.
This patch uses the application context instead, unless it's
not available for some unlikely reason.

A possible symptom of this issue is to have Bluetooth tethering
failing with a security exception, because it's requested by
the "android" package without system uid.

Merged-In: Ib8815f010883cdb94fcad2cdfb237de39327b20a
Bug: 73572062
Change-Id: Id652c1625194dc73dcbf8dfcad4b4e2e6fbebf4e

core/java/android/app/ActivityThread.java

@@ -963,7 +963,8 @@ public final class ActivityThread {
         }
 
         public void setHttpProxy(String host, String port, String exclList, Uri pacFileUrl) {
-            final ConnectivityManager cm = ConnectivityManager.from(getSystemContext());
+            final ConnectivityManager cm = ConnectivityManager.from(
+                getApplication() != null ? getApplication() : getSystemContext());
             final Network network = cm.getBoundNetworkForProcess();
             if (network != null) {
                 Proxy.setHttpProxySystemProperty(cm.getDefaultProxy());