vmxnet3: Enable GRO support.

vmxnet3: Enable GRO support.

When receiving packets from another guest on the same hypervisor, it's
generally possible to receive large packets because no segmentation is
necessary and these packets are handled by LRO.  However, when doing
routing or bridging we must disable LRO and lose this benefit.  In
these cases GRO can still be used and it is very effective because the
packets which are segmented in the hypervisor are received very close
together and can easily be merged.

CC: Shreyas Bhatewara <sbhatewara@vmware.com>
CC: Scott Goldman <scottjg@vmware.com>
CC: VMware PV-Drivers <pv-drivers@vmware.com>
Signed-off-by: Jesse Gross <jesse@nicira.com>
Signed-off-by: Scott J. Goldman <scottjg@vmware.com>
Signed-off-by: David S. Miller <davem@davemloft.net>