interface: Add functions to get sriov PF/VF relationship of a net interface

interface: Add functions to get sriov PF/VF relationship of a net interface

This patch adds the following functions to get PF/VF relationship of an SRIOV
network interface:
ifaceIsVirtualFunction: Function to check if a network interface is a SRIOV VF
ifaceGetVirtualFunctionIndex: Function to get VF index if a network interface is a SRIOV VF
ifaceGetPhysicalFunction: Function to get the PF net interface name of a SRIOV VF net interface

Signed-off-by: Roopa Prabhu <roprabhu@cisco.com>
Signed-off-by: Christian Benvenuti <benve@cisco.com>
Signed-off-by: David Wang <dwang2@cisco.com>