Previously the rate controller disabled updating the integral below 20%
throttle. This is not ideal for several reasons:
- some racers already hover with 20% throttle.
- for acro it is important to always keep the integral enabled, it has a
  noticeable effect on flight performance.

It's now the same way as in the ARM logic further down.

A reason for using switch arming in the first place is that you cannot
accidentally disarm in-air with the sticks during acrobatic flights.

It also adds a low-throttle arming requirement for switch arming.

This changes the arming logic such that the preflight checks don't need
to be satisfied if arming happens < 5 seconds after the last disarming.
This allows to recover from accidental in-air disarming.

if fRunPreArmChecks was set to false, there were still cases where the
preflight checks could be called. This fixes that.

arming_state_transition() with fRunPreArmChecks=false is only called
when entering & leaving preflight calibration mode.
All other places use fRunPreArmChecks=true, which means there is no change
for these.

- this matches the logic in arming_state_transition()
- if Commander::preflight_check was run in armed state and the checks
  failed, disarming was not possible anymore
  (because disarming checks for condition_system_sensors_initialized).
  That is currently not the case, but the existing logic is way too fragile.

Alternative solution: check if armed in Preflight::preflightCheck, and
only transition to false if disarmed (but also respect the re-arming
grace period).

- libuavcan in PX4/Firmware (fab974fde713b9de0ece1b85239d9dc52622052e): https://github.com/UAVCAN/libuavcan/commit/231b221b64265db4e98f86e53721316f9e17e143
    - libuavcan current upstream: https://github.com/UAVCAN/libuavcan/commit/dfcdf22eda16ff06847976fd6c7f40671fc92eb5
    - Changes: https://github.com/UAVCAN/libuavcan/compare/231b221b64265db4e98f86e53721316f9e17e143...dfcdf22eda16ff06847976fd6c7f40671fc92eb5

    dfcdf22 2018-06-26 Pavel Kirienko - Merge pull request #142 from thirtytwobits/feature/issue141
529a376 2018-06-21 Dixon, Scott - Issue #141 Add Vagrantfile to automate dev environment

Displays all enabled streams and their configured rates.
Example output:
instance #1:
        Name                Rate Config (current) [Hz] Message Size (if active) [B]
        HEARTBEAT                       1.00 (1.000)    21
        STATUSTEXT                     20.00 (6.320)
        COMMAND_LONG                  unlimited
        ALTITUDE                        1.00 (0.316)
        ATTITUDE                       25.00 (7.900)    40
        ATTITUDE_TARGET                10.00 (3.160)    49
        ESTIMATOR_STATUS                1.00 (0.316)    44
        EXTENDED_SYS_STATE              1.00 (0.316)    14
        GLOBAL_POSITION_INT            10.00 (3.160)    40
        GPS_RAW_INT                     1.00 (0.316)    62
        HOME_POSITION                   0.50 (0.158)
        RC_CHANNELS                     5.00 (1.580)
        SERVO_OUTPUT_RAW_0              1.00 (0.316)    49
        SYS_STATUS                      5.00 (1.580)    43
        SYSTEM_TIME                     1.00 (0.316)    24
        VFR_HUD                        25.00 (7.900)    32
        WIND_COV                        2.00 (0.632)

This implementation does not need more resources.
It's not super efficient in terms of runtime, but it's also not something
that is called often.

- add datarate
- add UDP remote port
- add partner IP

Plus correct return value.
Iridium links are below that.

 LandDetector FW: Fix param min/max values and descriptions as well as some variable names which were wrong/outdated (#9708)

* ecl: Update to version allowing use of flow sensors without gyros

* msg: Update description for optical_flow

Adds advice for publishing gyro rate integral message when no rate gyro is fitted.

Uninitialized `_ping_stats.last_ping_time` caused ping statistics to be printed even when no ping was received.

The uorb subscribe logic got changed for queued topics with
https://github.com/PX4/Firmware/pull/9436, meaning an orb_subscribe will
return past messages as well now.

This lead to an error 'Command denied during calibration' for the previously
received calibration start command.

This sets all channels to zero, including unused channels. Any consumer of the data using the channel count will not see a difference, but this is helpful to avoid confusion in log analysis.

   Refactored for efficiency and simplicity.

contains:
- https://github.com/PX4/ecl/pull/460
- https://github.com/PX4/ecl/pull/462

Because _pins[i] is set from parameter value - 1