CA-137227: Checking xen-backend in link of /sys/class/net/*/device/driver to identify vifs

Signed-off-by: Ravi Pandey <ravi.pandey@citrix.com>
Merge pull request #161 from ravippandey/ca-137227

 CA-137227: Checking xen-backend in link of /sys/class/net/*/device/driver to identify vifs