Fix crash bug with mismatched iface names

The copied-to LinkProperties needs the same iface name as the copied from.
Since we were copying into an empty LP this was trivial, but I
changed the params to tighten up this contract - don't want to
accidentally change an LP's iface name when we shouldn't.

bug:8569797
Change-Id: I5f88826e37271a0549c14d004bb2f16983b950e6