Initial import
Rename vapp to vhost and make more snabb integration friendly
vhost -q will require socket path
SET_VRING_NUM will setup the actual vring size
Add support for virtio_net_hdr
Update for v5 of QEMU patch

VhostUserMsg:
 - flags, lower 2 bits hold version (0x1 currently). bit 2 holds Reply bit
 - new field - size to hold the size of the following buffer (i.e. structures)

Add new message type VHOST_USER_ECHO. Handle it on the server side (send reply back).

vhost_user_send_fds - send only the requested message size
vhost_user_recv_fds - 2 step receive (hdr + buffer)

client/server - set proper message flags (version, reply bits)
Update for v6 of QEMU patch

VhostUserMsg:
 - remove fd and file members of the union

The fds are passed only thorugh the ancillary data.
The related idx from file structure is passed as u64.
Merge branch 'master' of git.tvelocity.eu:snabb/vapp