Fix NPE in restoring network policies

When backing up network policies, we write null for policies that are
null or are inferred. When restoring, this sends null policies to be set
which results in a NPE.

Bug: 79961560
Test: 1) atest NetworkPolicyManagerServiceTest
2) Manual: adb restore using backup set with null policies does not
crash

Change-Id: I450685e38acae0658ea984b86ca8b17ca27a71a6
diff --git a/services/core/java/com/android/server/net/NetworkPolicyManagerService.java b/services/core/java/com/android/server/net/NetworkPolicyManagerService.java
index 5bd7c0b..ab482bb 100644
--- a/services/core/java/com/android/server/net/NetworkPolicyManagerService.java
+++ b/services/core/java/com/android/server/net/NetworkPolicyManagerService.java
@@ -2706,6 +2706,9 @@
     private void normalizePoliciesNL(NetworkPolicy[] policies) {
         mNetworkPolicy.clear();
         for (NetworkPolicy policy : policies) {
+            if (policy == null) {
+                continue;
+            }
             // When two normalized templates conflict, prefer the most
             // restrictive policy
             policy.template = NetworkTemplate.normalize(policy.template, mMergedSubscriberIds);