[PATCH] ixp2000: fix gcc4 breakage

gcc4 doesn't like us declaring a static function inside another
function.  We can do away with this construct altogether and use
BUILD_BUG_ON() instead (idea from Andi Kleen.)

Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>