virPCIGetVirtualFunctions: Fetch also network interface name if needed

virPCIGetVirtualFunctions: Fetch also network interface name if needed

'virNetDevGetVirtualFunctions' calls 'virPCIGetVirtualFunctions' and
then re-iterates the returned list to fetch the interface names for the
returned virtual functions.

If we move the fetching of the interface name into
virPCIGetVirtualFunctions we can simplify the code and remove a bunch of
impossible error states.

To accomplish this the function is renamed to
'virPCIGetVirtualFunctionsFull' while keeping a wrapper with original
name and if the physical port ID is passed the interface name is fetched
too without the need to re-convert the address into a sysfs link.

For now 'virNetDevGetVirtualFunctions' still converts the returned data
into two lists.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>