Commit 8d8fc29d changed the behavior of slave
devices in regards to netpoll.  Specifically it created a mutually exclusive
relationship between being a slave and a netpoll-capable device.  This creates
problems for KVM because guests relied on needing netconsole active on a slave
device to a bridge.  Ideally libvirtd could just attach netconsole to the bridge
device instead, but thats currently infeasible, because while the bridge device
supports netpoll, it requires that all slave interface also support it, but the
tun/tap driver currently does not.  The most direct solution is to teach tun/tap
to support netpoll, which is implemented by the patch below.

I've not tested this yet, but its pretty straightforward.
Signed-off-by: NNeil Horman <nhorman@tuxdriver.com>
Reported-by: NRik van Riel <riel@redhat.com>
CC: Rik van Riel <riel@redhat.com>
CC: Maxim Krasnyansky <maxk@qualcomm.com>
CC: Cong Wang <amwang@redhat.com>
CC: "David S. Miller" <davem@davemloft.net>
Reviewed-by: NRik van Riel <riel@redhat.com>
Tested-by: NRik van Riel <riel@redhat.com>
Reviewed-by: NWANG Cong <amwang@redhat.com>
Signed-off-by: NDavid S. Miller <davem@conan.davemloft.net>