1. Solve the problem mentioned in revision 1623 (runtime error) 
   - Cause: In the EFM32 demo application, some TCP/IP functions are called in non-task context (e.g. "tcp_new()"). And after revision 1621, those functions will trigger the scheduler ("rt_schedule()") which seems to be triggered only in task context. 

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@1624 bbd45198-f89e-11dd-88c7-29a3b14d5316