Net driver using virtio

The network driver uses two virtqueues: one for input packets and one
for output packets.  This has nice locking properties (ie. we don't do
any for recv vs send).

TODO:
	1) Big packets.
	2) Multi-client devices (maybe separate driver?).
	3) Resolve freeing of old xmit skbs (Christian Borntraeger)

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: netdev@vger.kernel.org

drivers/net/Kconfig

@@ -3100,4 +3100,10 @@ config NETPOLL_TRAP
 config NET_POLL_CONTROLLER
 	def_bool NETPOLL
 
+config VIRTIO_NET
+	tristate "Virtio network driver (EXPERIMENTAL)"
+	depends on EXPERIMENTAL && VIRTIO
+	---help---
+	  This is the virtual network driver for lguest.  Say Y or M.
+
 endif # NETDEVICES

drivers/net/Makefile

@@ -243,3 +243,4 @@ obj-$(CONFIG_FS_ENET) += fs_enet/
 
 obj-$(CONFIG_NETXEN_NIC) += netxen/
 obj-$(CONFIG_NIU) += niu.o
+obj-$(CONFIG_VIRTIO_NET) += virtio_net.o