Move hidden APIs into system APIs

To allow vendor code to construct LinkAddress, which is
one of the parameter in the system API DataCallResponse.

Test: Build
Bug: 73659459
Merged-In: I3e203781d3a03285fa0e047cc8837ccb4a09016a
Change-Id: I3e203781d3a03285fa0e047cc8837ccb4a09016a