Merge branch 'xen-netback-leaks'

Igor Druzhinin says:

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xen-netback: fix memory leaks on XenBus disconnect

Just split the initial patch in two as proposed by Wei.

Since the approach for locking netdev statistics is inconsistent (tends not
to have any locking at all) accross the kernel we'd better to rely on our
internal lock for this purpose.
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Signed-off-by: David S. Miller <davem@davemloft.net>