[PDF] Fix link speed for virtual PODs

[PDF] Fix link speed for virtual PODs

ethtool reports the link speed as 'unknown' for said devices.
The only (current) consumer of this information is Fuel's new VPP
support, which detects all these interfaces as 'Gigabit', so align
our definitions in order to be able to dynamically construct the
VPP interface names based on PDF (link speed) + IDF (PCI bus).

While at it, add a new j2 macro helper to be used by Fuel installer.

Change-Id: Id6a52bbb7b86bbe3db2a81bb91ac378c6876ffc0
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>