Set setCurrentProxyScriptUrl as public

PacManager is part of services.jar, while ProxyManager is in
service-connectivity.jar. setCurrentProxyScriptUrl cannot be
package-private and called across jars.

As part of modularization of service-connectivity.jar, the
PacManager interface will then be formally defined.

Bug: 171540887
Test: Splitting service-connectivity, ProxyManager can reference the
      method
Change-Id: Ie41a5b569a119f305bf647e55a65febbde459352

services/core/java/com/android/server/connectivity/PacManager.java

@@ -177,7 +177,7 @@ public class PacManager {
      * @param proxy Proxy information that is about to be broadcast.
      * @return Returns whether the broadcast should be sent : either DO_ or DONT_SEND_BROADCAST
      */
-    synchronized boolean setCurrentProxyScriptUrl(ProxyInfo proxy) {
+    public synchronized boolean setCurrentProxyScriptUrl(ProxyInfo proxy) {
         if (!Uri.EMPTY.equals(proxy.getPacFileUrl())) {
             if (proxy.getPacFileUrl().equals(mPacUrl) && (proxy.getPort() > 0)) {
                 // Allow to send broadcast, nothing to do.