wifi(vts): Ignore HAL stop failure

The stop may fail if the interface down operation takes too long on some
devices. This is not fatal as long as we're able to bring up the
interfae for the next HAL start.

Bug: 68303248
Test: VTS tests
Change-Id: I93943f9d0cfb83cf07253c6f9b3866d6d137028f
1 file changed