fix home position timestamp to be the timestamp that the home was set and not when the message was sent

zeroed uninitialized fields on home_position, mavlink_rc_channels_override, mavlink_mission_item, mavlink_mission_item_int

It turns out that `sendto` does not work for TCP on Cygwin-Windows,
instead we need to use `send`. This required some refactoring since we
need to have the internet protocol and the port stored as a member
variable.

This should fix that lockstep SITL simulation was not working on
Windows.

    - micro-CDR in PX4/Firmware (b043cfac5e8635d9017ad6a13f45795ad6fda6fb): https://github.com/eProsima/micro-CDR/commit/8b3546e8848e4c07c16ec55730d3ad1aa94396ab
    - micro-CDR current upstream: https://github.com/eProsima/micro-CDR/commit/7a76880f90dfe702f4fa1723e22d1dcb491d7b9e
    - Changes: https://github.com/eProsima/micro-CDR/compare/8b3546e8848e4c07c16ec55730d3ad1aa94396ab...7a76880f90dfe702f4fa1723e22d1dcb491d7b9e

    7a76880 2018-12-11 Julián Bermúdez Ortega - Badges (#24)

- the flash-backend is selected by specifying nullptr as file or -1 as fd
- the default file is nullptr, and thus the FLASH
- 'param select' has no effect, FLASH is always the default

Thus there should be no functional change to existing setups.

Now that the lockstep changes are merged to master.

It turns out the noise of the airspeed depends on the least significant
bit of time which is now always 0 because time is quite regular with
lockstep. Therefore, we need a better source for the randomness. I chose
to use the sign of the y-gyro and it seems to work.

For the non-lockstep case we want to use CLOCK_MONOTONIC if possible.

Instead of using the define __PX4_POSIX_SITL it makes more sense to have
a define just to determine if the lockstep scheduler should be used.

The -t argument had been deleted because I didn't realize that it was
actually being used. Therefore, this brings it back and we now use -c
for TCP.

This is not suposed to ever trigger anyway.

@bkueng reviewed this and found that it is dangerous to continue on
timeout because we don't update other gyro sensors in the timeout case.

According to @bkueng this was to schedule other processes but can now be
removed.

The new board config changed everything, so I needed to move the
lockstep_scheduler repo.

Consistency over taste :(.

Who knows what this really is.

Hopefully, we can fix the defines for macOS.

The files are copied from:
https://github.com/julianoes/lockstep-scheduler/

Fixes the unit test on macOS.

This brings a couple more build fixes.

This makes sure lockstep is only built for SITL builds and fixes the
existing builds.

These symbols were duplicated all over the place.

It turns out Mac OS X v10.11.6 (El Capitan) is still covered by security
updates at this time, so not end-of-lifed, so we might as well keep
these legacy things.

When `connect()` fails, the state of the socket is unspecified and we
need to close the it and create it again.

It turns out retrying connect worked on Linux but it didn't on macOS.