Allow background networking for test uids

These tests try to run as uids 99999 and 99998 which need to be exempt
from the BACKGROUND_MATCH allowlist chain which can be enabled at boot.

Test: atest resolv_integration_test
Test: atest resolv_unit_test

Bug: 304347838
Bug: 325150155
Change-Id: Ia989304877b661182129c2c49986205733f6a609