Fix issue of PF brought down if VF is 8021.Qbh and pci passthrough

Fix issue of PF brought down if VF is 8021.Qbh and pci passthrough

If a 8021.Qbh network device supports SRIOV and its VF is being used
in pci passthrough mode, when the guest is shutdown or destroyed, the
PF inteface is also brought down. qemuDomainHostdevNetConfigRestore()
finds out the PF for provided hostdev (which is VF) and passes it to
virNetDevPortProfileDisassociate() as linkdev. Later, linkdev gets passed
to virNetDevSetOnline() where the interface is brought down by clearing
IFF_UP flag.

Bringing down a PF, when only VF is being brought down is not expected
behavior. This patch adds a check so that virNetDevSetOnline() is called
only for PF and not if device is a VF.

Signed-off-by: Nishank Trivedi <nistrive@cisco.com>