Ignore potential SystemProperties errors when setting net.dns

Test: as follows
    - built
    - flashed
    - booted
    - "runtest frameworks-net" passes
Bug: 33308258
Bug: 36249702

Change-Id: I76ae853ceb61b7b900f36f9c3cd67b2d2284aab0
(cherry picked from commit 4edba01eb4c05c0a9872014255e9e46c60463fd9)

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

@@ -4470,17 +4470,24 @@ public class ConnectivityService extends IConnectivityManager.Stub
         int last = 0;
         for (InetAddress dns : dnses) {
             ++last;
-            String key = "net.dns" + last;
-            String value = dns.getHostAddress();
-            mSystemProperties.set(key, value);
+            setNetDnsProperty(last, dns.getHostAddress());
         }
         for (int i = last + 1; i <= mNumDnsEntries; ++i) {
-            String key = "net.dns" + i;
-            mSystemProperties.set(key, "");
+            setNetDnsProperty(i, "");
         }
         mNumDnsEntries = last;
     }
 
+    private void setNetDnsProperty(int which, String value) {
+        final String key = "net.dns" + which;
+        // Log and forget errors setting unsupported properties.
+        try {
+            mSystemProperties.set(key, value);
+        } catch (Exception e) {
+            Log.e(TAG, "Error setting unsupported net.dns property: ", e);
+        }
+    }
+
     private String getNetworkPermission(NetworkCapabilities nc) {
         // TODO: make these permission strings AIDL constants instead.
         if (!nc.hasCapability(NET_CAPABILITY_NOT_RESTRICTED)) {