SRIOV NIC offload feature discovery

SRIOV NIC offload feature discovery

Adding functionality to libvirt that will allow it
query the ethtool interface for the availability
of certain NIC HW offload features

Here is an example of the feature XML definition:

<device>
<name>net_eth4_90_e2_ba_5e_a5_45</name>
  <path>/sys/devices/pci0000:00/0000:00:03.0/0000:08:00.1/net/eth4</path>
  <parent>pci_0000_08_00_1</parent>
  <capability type='net'>
    <interface>eth4</interface>
    <address>90:e2:ba:5e:a5:45</address>
    <link speed='10000' state='up'/>
    <feature name='rx'/>
    <feature name='tx'/>
    <feature name='sg'/>
    <feature name='tso'/>
    <feature name='gso'/>
    <feature name='gro'/>
    <feature name='rxvlan'/>
    <feature name='txvlan'/>
    <feature name='rxhash'/>
    <capability type='80203'/>
  </capability>
</device>

Signed-off-by: Ján Tomko <jtomko@redhat.com>