If the filter was disabled, the apply() would always return 0.

in order to not constantly switch mag fusion mode in gusty winds.

    - nuttx in PX4/Firmware (31767b6b5aeb4293c2991dbfea6b810e34a34149): https://github.com/PX4/NuttX/commit/999c4357a220d9ea271475e74abd5d8ba080be27
    - nuttx current upstream: https://github.com/PX4/NuttX/commit/166d898c70141d7ddb179b5ead1c5ea726574411
    - Changes: https://github.com/PX4/NuttX/compare/999c4357a220d9ea271475e74abd5d8ba080be27...166d898c70141d7ddb179b5ead1c5ea726574411

166d898 2018-10-18 Daniel Agar - [BACKPORT] Merged in dagar/nuttx/pr-stm32_dma_per_spi (pull request #736)
0a5b1cb 2018-10-17 David Sidrane - [BACKPORT] Lampoo-master-spi-flash (pull request #735)

    - ecl in PX4/Firmware (bd71d1cd9e1e1d29f89351c43f879e6c49b727bc): https://github.com/PX4/ecl/commit/f240eaa5b089c50b957a3ab61aeb722ea57dccd9
    - ecl current upstream: https://github.com/PX4/ecl/commit/10a0fef7b7db749f5baf3384e9c900d3aa0e8140
    - Changes: https://github.com/PX4/ecl/compare/f240eaa5b089c50b957a3ab61aeb722ea57dccd9...10a0fef7b7db749f5baf3384e9c900d3aa0e8140

    10a0fef 2018-10-18 jie.zhang - EKF/control: remove unnecessary yaw_align update
8bbaf89 2018-10-17 Daniel Agar - EKF add new simple setIMUData() interface (#512)
e6cd6ef 2018-09-03 Paul Riseborough - EKF: Fix bug preventing  use of flow sensors without gyros
2c3a064 2018-09-18 Daniel Agar - README.md update Jenkins build status icon and url

removed px4_poll, something changed and broke the way I was using it. This has been tested successfully