fix per esp8266#6039 (comment) @mhightower83

Author: d-a-v

cores/esp8266/Arduino.h

@@ -169,7 +169,7 @@ void ets_intr_unlock();
 #define lockLeaveVar(varSave)        __asm__ __volatile__("wsr %0,ps; isync" :: "a" (varSave) : "memory")
 
 #define lockDeclM()  uint32_t intrState
-#define lockEnterM() lockEnterVar(intrState, 0)
+#define lockEnterM() lockEnterVar(intrState, 15)
 #define lockLeaveM() lockLeaveVar(intrState)
 
 #define lockEnter() lockDeclM(); lockEnterM()

cores/esp8266/Schedule.cpp

@@ -54,10 +54,11 @@ bool schedule_function_us(mFuncT fn, uint32_t repeat_us)
     item->mNext = sFirst;
     sFirst = item;
 
+    lockLeave();
+
     if (repeat_us)
         item->callNow.reset(repeat_us);
 
-    lockLeave();
     return true;
 }