net: Adding netmap network backend

This patch adds support for a network backend based on netmap.
netmap is a framework for high speed packet I/O. You can use it
to build extremely fast traffic generators, monitors, software
switches or network middleboxes. Its companion software switch
VALE lets you interconnect virtual machines.
netmap and VALE are implemented as a non-intrusive kernel module,
support NICs from multiple vendors, are part of standard FreeBSD
distributions and available in source format for Linux too.

To compile QEMU with netmap support, use the following configure
options:
    ./configure [...] --enable-netmap --extra-cflags=-I/path/to/netmap/sys
where "/path/to/netmap" contains the netmap source code, available at
    http://info.iet.unipi.it/~luigi/netmap/

The same webpage contains more information about the netmap project
(together with papers and presentations).

Signed-off-by: Vincenzo Maffione <v.maffione@gmail.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
MAINTAINERS: Add netmap maintainers

Signed-off-by: Vincenzo Maffione <v.maffione@gmail.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
virtio-net: don't update mac_table in error state

mac_table was always cleaned up first in handling
VIRTIO_NET_CTRL_MAC_TABLE_SET command, and we din't recover
mac_table content in error state, it's not correct.

This patch makes all the changes in temporal variables,
only update the real mac_table if everything is ok.
We won't change mac_table in error state, so rxfilter
notification isn't needed.

This patch also fixed same problame in
 http://lists.nongnu.org/archive/html/qemu-devel/2013-11/msg01188.html
 (not merge)

I will send patch for virtio spec to clarifying this change.

Signed-off-by: Amos Kong <akong@redhat.com>
Reviewed-by: Vlad Yasevich <vyasevic@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
net: Update netdev peer on link change

When a link change occurs on a backend (like tap), we currently do
not propage such change to the nic.  As a result, when someone turns
off a link on a tap device, for instance, then a guest doesn't see
that change and continues to try to send traffic or run DHCP even
though the lower-layer is disconnected.  This is OK when the network
is set up as a HUB since the the guest may be connected to other HUB
ports too, but when it's set up as a netdev, it makes thinkgs worse.

The patch addresses this by setting the peers link down only when the
peer is not a HUBPORT device.  With this patch, in the following config
  -netdev tap,id=net0 -device e1000,mac=XXXXX,netdev=net0
when net0 link is turned off, the guest e1000 shows lower-layer link
down. This allows guests to boot much faster in such configurations.
With windows guest, it also allows the network to recover properly
since windows will not configure the link-local IPv4 address, and
when the link is turned on, the proper address address is configured.

Signed-off-by: Vlad Yasevich <vyasevic@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>