Virtio features

This is a merge of the following branches/features:

 - "old" MQ branch - implementing ANY_LAYOUT, VQ/MQ and INDIRECT_DESCRIPTORS
 - Antonio's v-mq branch - where he improves the MQ branch performance with some luajit trickery
 - the "new" MRG_RXBUF support

The current performance of this branch is (10e7 64byte packets):
On 0000:05:00.0 got 3.699
On 0000:82:00.0 got 3.547
On 0000:84:00.0 got 3.517
On 0000:88:00.0 got 3.616
Rate(Mpps):     14.379