Previously the acceptance radius was 0, so the FlightTaskAutoLine was
randomly changing yaw and sometimes going into a random direction.
There is still something else wrong in there, but avoids the reposition
problem.

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)