Add a unit test to verify that BPF coordinator access downstream4
and upstream4 map while the conntrack event was received.
Verify shim API for IPv4:
- tetherOffloadRuleAdd
- tetherOffloadRuleRemove
- tetherOffloadGetAndClearStats
- tetherOffloadSetInterfaceQuota
- isAnyIpv4RuleOnUpstream
Test: atest TetheringCoverageTests
Change-Id: Ia57f07990d8750fd6ff67d7f4a18aa610336024a