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: Id1498fb8627dd7221a5ab7cde72929e6ee25b425
Change-Id: Id1498fb8627dd7221a5ab7cde72929e6ee25b425
(cherry picked from commit 7ff7865d)