net: xen-netback: correctly restart Tx after a VM restore/migrate

net: xen-netback: correctly restart Tx after a VM restore/migrate

If a VM is saved and restored (or migrated) the netback driver will no
longer process any Tx packets from the frontend.  xenvif_up() does not
schedule the processing of any pending Tx requests from the front end
because the carrier is off.  Without this initial kick the frontend
just adds Tx requests to the ring without raising an event (until the
ring is full).

This was caused by c3e4c0b0b47b9f925b5831fea42af76acc29693a (net:
xen-netback: convert to hw_features) which reordered the calls to
xenvif_up() and netif_carrier_on() in xenvif_connect().

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>