Add flag in isInternetDataAllowed() function

- Skip existed networks check when data out of service.
Doc: go/dsrm-improve
Bug: 284420611
Test: Test passed by reporter. (b/284420611#comment28)

Change-Id: Ic9880a9b24b869b82b9b6fbfd476d74cc5788d39
diff --git a/flags/data.aconfig b/flags/data.aconfig
index 267048e..a74d279 100644
--- a/flags/data.aconfig
+++ b/flags/data.aconfig
@@ -90,3 +90,10 @@
   description: "Collect vonr status in voice call metric"
   bug:"288449751"
 }
+
+flag {
+  name: "ignore_existing_networks_for_internet_allowed_checking"
+  namespace: "telephony"
+  description: "Ignore existing networks when checking if internet is allowed"
+  bug: "284420611"
+}