Google RoT: avoid potential dangling pointer

The struct |ResolvedEntity| stores a pointer which might be dangling in
the future when interface is not longer a string literal. Given that the
interface string is small enough, this commits changes the data member
to a string which is constructed (copied) from the string literal today.

Tested: trivial change. Compiles.

Signed-off-by: Nan Zhou <nanzhoumails@gmail.com>
Change-Id: I2759635f7fa296cc8aa141735efb3799a1503726