Bug 1426474 - Turn on TFO only for Darwin 17.3 and later. r=hurley

modules/libpref/init/all.js

@@ -4782,7 +4782,7 @@ pref("network.tcp.keepalive.retry_interval", 1); // seconds
 pref("network.tcp.keepalive.probe_count", 4);
 #endif
 
-#if defined(XP_WIN)
+#if defined(XP_WIN) || defined(XP_MACOSX)
 pref("network.tcp.tcp_fastopen_enable", true);
 #else
 pref("network.tcp.tcp_fastopen_enable", false);

netwerk/protocol/http/nsHttpHandler.cpp

@@ -343,7 +343,7 @@ nsHttpHandler::SetFastOpenOSSupport()
     if (NS_SUCCEEDED(rv)) {
         // set min version minus 1.
 #if XP_MACOSX
-        int min_version[] = {15, 0};
+        int min_version[] = {17, 3};
 #elif ANDROID
         int min_version[] = {4, 4};
 #elif XP_LINUX