The if_at91.c driver sometime don't mark buffers from broken packets as
free. And the sequential.c don't call the driver in every case. The two
uploaded files correct this. Its not an patch because i use the files
currently in my project and not in the ecos repository. 

An other thing the lwIP from ecos is missing is the check if the
kernel-mailbox-size is at least the size of the PBUF or INPKT buffer... 

The new version of the if_at91.c deliver-procedure tests all the buffers
of the EMAC at once and search also for broken packets. There was also an
error in the calculation of the packet-size if the packets where bigger
then 128bytes.