Add WithLoadSwIfIndex option to up chain element

[glazychev-art]

Context

networkservicemesh/cmd-nse-vl3-vpp#1

Description

We are currently using ifindex.Load(...) inside up chain element to get the swIfIndex to up the interface.
For loopback interface we need to use loopback.Load instead of ifindex.Load

To make this possible, we need to add the option:

func WithLoadSwIfIndex(func(ctx context.Context, isClient bool) (value interface_types.InterfaceIndex, ok bool)) Option {...}