Delay test for APF activation after screen-off

CTS tests screen-on device in the beginning, but APF is not activated after screen-off in the test setup.
This change adds 3 secs delay to ensure APF activation before test execution.

Bug: 402667362
Test: ./cts-tradefed run cts-on-gsi -m CtsConnectivityMultiDevicesTestCases -t ApfV4Test --shard-count 2
Test: atest CtsConnectivityMultiDevicesTestCases:ApfV4Test
Change-Id: I067ce792b5f89e2f0051933982ebc734607fbf98
1 file changed