aconfig: cpp test-mode lib

Incompatible interface between test-mode and normal mode.

Bluetooth is linking the normal flag for the code that is shipped, and
it is linking the test-mode library for unit testing.
While trying to move some test to use the test-mode, we noticed some
failure as the flag returned were not the one expected.

It appear the code and the test are built against 2 different library,
but linked against one.
The provide interface only contains getter in normal mode, and it is
alternating between getter/setter in test-mode.
By moving the setter in test-mode toward the end of the interface, we
are not modifying the assumed order for the code built against the
normal mode.

This CL is a short term fix, to make the test goes green and prevent
immediat failure. An refactor of the cpp generated code should be done
to avoid using 2 different version of the same symbol in 2 different
libs.

Bug: 311772251
Test: atest aconfig.test
Change-Id: I97f6523452c451d005d2e92bfa1ef861611ab840