net: Enable TSO if supported by at least one device

As it stands users of netdev_compute_features (e.g., bridges/bonding)
will only enable TSO if all consituent devices support it.  This
is unnecessarily pessimistic since even on devices that do not
support hardware TSO and SG, emulated TSO still performs to a par
with TSO off.

This patch enables TSO if at least on constituent device supports
it in hardware.

The direct beneficiaries will be virtualisation that uses bridging
since this means that TSO will always be enabled for communication
from the host to the guests.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>