Fixed incorrect metered/unmetered APN in AP-assisted mode

From now all data traffic through IWLAN will be unmetered. Only
data through cellular will be checked for metered/unmetered.

Test: Unit tests
Bug: 132433959
Merged-In: I6947e9ba9a461484c25ca884048939724be7ce30
Change-Id: I6947e9ba9a461484c25ca884048939724be7ce30
(cherry picked from commit 552fc09c)