Description of problem:
Large receive offload is a feature that isn't supported by Linux bridges, nor virtio backend drivers. If a physical NIC has LRO enabled by default, you'll get dropped packets on the host

eth3: received packets cannot be forwarded while LRO is enabled
eth3: received packets cannot be forwarded while LRO is enabled
eth3: received packets cannot be forwarded while LRO is enabled

Thus we need to be able to disable LRO on physical NICs.

The ifcfg-xxx files appears to support these settings, albeit with a deprecated option

   Deprecated, but supported:
    ETHTOOL_OPTS=...
      Any device-specific options supported by ethtool. For example,
      if you wanted to force 100Mb full duplex:
        ETHTOOL_OPTS="speed 100 duplex full autoneg off"
      Note that changing speed or duplex settings almost always
      requires disabling autonegotiation with 'autoneg off'.

      Long term, this should be done by sysadmin-written udev rules.

So we have two options

 - Expose this tunable via the interface XML (and by extension netcf) and use the deprecated setting
 - Expose this tunable via the node device APIs and create udev rules

We likely need to expose whether each physical NIC is capable of gro, lro, etc via the node device APIs in any case, otherwise you won't know whether the tunable is actually supported on the NIC in question.

This could push the balance in favour of a pure nodedevice API instead of nodedev + interface

Version-Release number of selected component (if applicable):
libvirt-0.8.2

How reproducible:
Hardware dependant

Steps to Reproduce:
1. Get a machine witha NIC supporting LRO
2. Enable LRO
3. Put the NIC into a bridge
4. Boot a guest with the bridge
5. Observe dropped packets
  
Actual results:


Expected results:


Additional info: