[27/06/2014] No changes
[27/06/2014]
1. Added eth.h, eth.c;
2. Every 5 second, check if eth is reconnected/disconnected: if
disconnected, do not receive frames
3. Should do a periodic task, instead of count times
[27/06/2014] If eth disconnected, not wakes up every 10ms. Instead, it
will wake up in 2s.