Bug 1706422 - Initiaize DNS service earlier, r=necko-reviewers,valentin

The problem here is that the creation of DNS service and setting trr pref is racy.
This problem can be fixed by creating DNS service earlier.

Differential Revision: https://phabricator.services.mozilla.com/D139106

netwerk/test/unit_ipc/test_dns_by_type_resolve_wrap.js

@@ -39,6 +39,12 @@ function setup() {
   // XXX(valentin): It would be nice to just call trr_test_setup() here, but
   // the relative path here makes it awkward. Would be nice to fix someday.
   addCertFromFile(certdb, "../unit/http2-ca.pem", "CTu,u,u");
+
+  if (!gDNS) {
+    gDNS = Cc["@mozilla.org/network/dns-service;1"].getService(
+      Ci.nsIDNSService
+    );
+  }
 }
 
 setup();