UCT: Add uct_iface_query_v2

[roiedanino]

What

Add uct_iface_query_v2, which is expandable thanks to the field mask

Why ?

We want to enable adding new fields to be queried using iface_query, and in order to remain backward compatible we need to use a field mask, the "old" uct_iface_query will call uct_iface_query_v2 and copy the values back into the v1 attr struct.