Refactoring hostside network restrictions tests

The definition of background can be fluid and ambiguous. Refactored all
code to be explicit about process states when making assertions.

No functional change is expected to tests.

Test: atest CtsHostsideNetworkTests

Bug: 304347838

Change-Id: Ibc614d74f46d436cad4586c1d309bbb3648b8eb1
Merged-In: Ibc614d74f46d436cad4586c1d309bbb3648b8eb1