Prevent opportunistic scans from changing the hardware filter

Before this patch opportunistic scans could set the hardware filter
to be an all pass filter. This would result large amounts of scan
results as short filtered scans would act as if they were unfiltered.
Now if an app is scanning opportunistically, its filter doesn't
get added to the hardware filter.

Bug: 62280037
Test: Do a filtered scan while another app is scanning opportunistically
      and see that the scan results only increase marginally.

Change-Id: I6214a2dd14d2c5ee4c21faa440c48ce7bab0b3fe