[netdrvr] remove unnecessary #include

The drivers below do not use LINUX_VERSION_CODE nor KERNEL_VERSION.
  drivers/net/acenic.c
  drivers/net/bnx2x_link.c
  drivers/net/bnx2x_main.c
  drivers/net/cpmac.c
  drivers/net/gianfar_sysfs.c
  drivers/net/ipg.h
  drivers/net/ppp_mppe.c
  drivers/net/pppol2tp.c
  drivers/net/r6040.c
  drivers/net/sh_eth.c
  drivers/net/sky2.c
  drivers/net/tehuti.h
  drivers/net/typhoon.c

This patch removes the said #include <linux/version.h>.

Signed-off-by: Huang Weiyi <hwy@cn.fujitsu.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>