Merge branch 'revert/revert_upgrade_lib' into 'master'

revert: revert libupgrade.a to 81bde69

See merge request sdk/ESP8266_NONOS_SDK!307

Author: xcguang

VERSION

@@ -6,7 +6,7 @@ gwen:
     net80211    :   1cef03c
     pp          :   865fa65
     ssl         :   865fa65
-    upgrade     :   865fa65
+    upgrade     :   81bde69
     wpa         :   1cef03c
     wpa2        :   865fa65
     wps         :   865fa65