Fix 'datagram SKIPPED' errors in EtherCAT kernel

When launching the CS, the PDOs seem to be correctly exchanged with the dish and the stirling PLCs. However, dmesg messages report many warnings, saying that many datagrams were skipped. After a quick search on the web, [1] suggests that it might be due to a timing issue.

[1] http://lists.etherlab.org/pipermail/etherlab-users/2009/000386.html