ethtool: do not set some flags, if others failed

NETIF_F_NTUPLE flag setting introduced a bug:  non-ntuple flags
like LRO may be successfully set, before ioctl(2) returns failure
to userspace.

The set-flags operation should be all-or-none, rather than leaving
things in an inconsistent state prior to reporting failure to
userspace.

Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>