- fixes #7911

 - avoid "exceeded maximum number of file descriptors" when "make posix gazebo_typhoon_h480"
 - closes #7892

Change units of parameters from uSec to sec.
Change recommended FW value for COM_POS_FS_GAIN from 2 to 0
Fix error in parameter description for COM_POS_FS_PROB
Fix error in unit for COM_POS_FS_GAIN

This is required because the hardcoded values were too sensitive for fixed wing use and bad initial mag heading could trigger the failsafe and lead to crashes on launch. The defaults have been left unchanged. Suitable values for fixed wing use will need to be implemented in the airframe specific config file.

 - this prevents constant land detector publications

Signed-off-by: Sugnan Prabhu S <sugnan.prabhu.s@intel.com>