Update isValidLockdownProfile to block PPTP

Since this isn't supported and it will take a framework update to make
it work.

Bug: 28807474
Change-Id: I12371134a1c51a53af26fe8c4db1f04b0f687abe

core/java/com/android/internal/net/VpnProfile.java

@@ -176,6 +176,11 @@ public class VpnProfile implements Cloneable, Parcelable {
      * connection.
      */
     public boolean isValidLockdownProfile() {
+        // b/7064069: lockdown firewall blocks ports that would be used for PPTP
+        if (type == TYPE_PPTP) {
+            return false;
+        }
+
         try {
             InetAddress.parseNumericAddress(server);