xen-netback: vif counters from int/long to u64

[ Upstream commit ebf692f85ff78092cd238166d8d7ec51419f9c02 ]

This patch fixes an issue where the type of counters in the queue(s)
and interface are not in sync (queue counters are int, interface
counters are long), causing incorrect reporting of tx/rx values
of the vif interface and unclear counter overflows.
This patch sets both counters to the u64 type.

Signed-off-by: Mart van Santen <mart@greenhost.nl>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>