Rename *Iface* APIs to *Interface*

Address API review feedback, other APIs have been refering to
these as "interface" instead of "iface" so migrate the APIs named
*Iface* to *Interface*.

Bug: 183972554
Test: atest android.net.UnderlyingNetworkInfoTest
Change-Id: I38b476e762fb57fa88c4a789092d0af6f5330d80