Merge branch 'xen-netback-fix-multiple-extra-info-handling'

Paul Durrant says:

====================
xen-netback: fix multiple extra info handling

If a frontend passes multiple extra info fragments to netback on the guest
transmit side, because xen-netback does not account for this properly, only
a single ack response will be sent. This will eventually cause processing
of the shared ring to wedge.

This series re-imports the canonical netif.h from Xen, where the ring
protocol documentation has been updated, fixes this issue in xen-netback
and also adds a patch to reduce log spam.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>