ethernet/neterion: use core min/max MTU checking

s2io: min_mtu 46, max_mtu 9600

vxge: min_mtu 68, max_mtu 9600

CC: netdev@vger.kernel.org
CC: Jon Mason <jdmason@kudzu.us>
Signed-off-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>