fixed the return value for sys_arch_mbox_fetch in lwip stack

components/net/lwip-1.4.1/src/arch/sys_arch.c

@@ -534,7 +534,7 @@ u32_t sys_arch_mbox_tryfetch(sys_mbox_t *mbox, void **msg)
     else
     {
         if (ret == RT_EOK)
-            ret = 1;
+            ret = 0;
     }
 
     return ret;

components/net/lwip-2.0.2/src/arch/sys_arch.c

@@ -544,7 +544,7 @@ u32_t sys_arch_mbox_tryfetch(sys_mbox_t *mbox, void **msg)
     else
     {
         if (ret == RT_EOK)
-            ret = 1;
+            ret = 0;
     }
 
     return ret;

components/net/lwip-2.0.3/src/arch/sys_arch.c

@@ -544,7 +544,7 @@ u32_t sys_arch_mbox_tryfetch(sys_mbox_t *mbox, void **msg)
     else
     {
         if (ret == RT_EOK)
-            ret = 1;
+            ret = 0;
     }
 
     return ret;

components/net/lwip-2.1.2/src/arch/sys_arch.c

@@ -558,7 +558,7 @@ u32_t sys_arch_mbox_tryfetch(sys_mbox_t *mbox, void **msg)
     else
     {
         if (ret == RT_EOK)
-            ret = 1;
+            ret = 0;
     }
 
     return ret;