bug 1432150 - restore rcwn pref after test_immutable.js test complete, r=mcmanus

The test previously only switched off the pref and didn't restore the
old value when done.

--HG--
extra : rebase_source : 87a769b3148f17b74f98c343743039b8d0d265c2

netwerk/test/unit/test_immutable.js

@@ -5,6 +5,7 @@ var prefs;
 var spdypref;
 var http2pref;
 var origin;
+var rcwnpref;
 
 function run_test() {
   var env = Cc["@mozilla.org/process/environment;1"].getService(Ci.nsIEnvironment);
@@ -18,6 +19,7 @@ function run_test() {
 
   spdypref = prefs.getBoolPref("network.http.spdy.enabled");
   http2pref = prefs.getBoolPref("network.http.spdy.enabled.http2");
+  rcwnpref = prefs.getBoolPref("network.http.rcwn.enabled");
 
   prefs.setBoolPref("network.http.spdy.enabled", true);
   prefs.setBoolPref("network.http.spdy.enabled.http2", true);
@@ -39,6 +41,7 @@ function run_test() {
 function resetPrefs() {
   prefs.setBoolPref("network.http.spdy.enabled", spdypref);
   prefs.setBoolPref("network.http.spdy.enabled.http2", http2pref);
+  prefs.setBoolPref("network.http.rcwn.enabled", rcwnpref);
   prefs.clearUserPref("network.dns.localDomains");
 }