VIA_VELOCITY: Don't oops on MTU change.

mainline: bd7b3f34

Simple mtu change when device is down.
Fix http://bugzilla.kernel.org/show_bug.cgi?id=9382

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Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Jeff Mahoney <jeffm@suse.com>
CC: Oliver Pinter <oliver.pntr@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>