Move NetworkStack AIDLs to NetworkStack folder

The AIDLs and ipmemorystore-client were already statically linked
libraries, so their location in the source tree does not change anything
(they were already built into the NetworkStack module and the
framework). It makes more sense to have them in the NetworkStack module
folder however, as changes to these files will be released with the same
cadence as the module, not the framework.

Bug: 139106271
Test: built, flashed, WiFi working
Change-Id: I886acae850a5e8a9a7bc3ca8aac8690d681ca2cd