CtsHostsideNetworkPolicyTests: Fix tests failing on HSUM

Several tests in the CtsHostsideNetworkPolicyTests module were
failing on Headless System User Model (HSUM) devices.

On HSUM devices, the test runs as a secondary user,
and shell commands need an explicit user ID to run against the
correct user.

This change fixes the issue by plumbing the correct user ID into
the shell commands used by the failing tests.

Flag: EXEMPT bugfix
Bug: 385614857
Test: atest HostsideRestrictBackgroundNetworkTests
Change-Id: Ic0793bec41d55188ab1197edd7c468603a2e3368