filter: use --switch=2 --readonly-tables gperf options

See 73ecb924379b8e665ee94235a353403c5d29eae6 (Use --switch=2
--readonly-tables gperf options, 2014-04-13) for reasoning.

Change-Id: Ic63747a6cd982557cad8470ae775afa4b3d8d883
sdext: use --switch=2 --readonly-tables gperf options

See 73ecb924379b8e665ee94235a353403c5d29eae6 (Use --switch=2
--readonly-tables gperf options, 2014-04-13) for reasoning.

Change-Id: Ie1cfe753979d908077134b86587d8de5fa7c2ee8