net: Fix IXP 2000 network driver building.

The IXP 2000 network driver was failing to build as it has its own
statistics gathering which was not compatible with the recent network
device operations changes. This patch fixes the driver in the obvious
way and has been compile tested. I have been unable to get the ixp2000
maintainer to comment or test this fix.

Signed-off-by: Vincent Sanders <vince@simtec.co.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>