if _ftp_on is true, message_buffer was created and read, but it was
actually never written to, so this is not needed. It can only ever be
written to if _forwarding_on is true.

And the maximum number of configured file descriptors.

Note that this is per group, not per thread, so that e.g. logger and
log_writer_file show the same number.

VDev::getDev() is used in px4_access, which is used in orb_exists. And if
the topic does not exist, it iterates over all 500 indexes, which is slow.
It was slow even if the topic existed, the map reduces runtime from linear
to logarithmic (there are around 80 items in the container).
This is only used on posix.

* Fixed memory leak (indicated by cppcheck) upstream

This allows to run a command / function once when being deactivated. This avoids having flight modes which are not active run unnecessary code all the time.

Adding files which enable a simulation with the autonomous underwater
vehicle (AUV) from the Technical University Hamburg-Harburg

inverted S.bus signal and fetch the data of each channel and publish it

2. Fix the bug of linux_pwm_out, when the protocol is pca9685,
after the init method is executed,the method of determining the return
value of init method is incorrect,this will cause the driver to fail

3. Add linux_sbus driver to other posix prefixes cmake files

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

There are bugs in version 2.05.1 (default version in Ubuntu 16.04)

Signed-off-by: Mark Charlebois <charlebm@gmail.com>