network: mvpp2 causes kernel panic under stress

[gclement]

The test consists in a lighttpd server + php-cgi running on the Armada
375, with a "stupid" PHP script doing:

And then from a remote machine, 5 or 6 infinite loops of wget
fetching the URL thats run this PHP script.
It makes the kernel crashes after few hours.

[tpetazzoni]

Note that this happens with the improvements patches from Marcin. Without those patches (i.e pure mainline), in crashes in a few minutes.