Update submodule v2.0 to latest Sat Dec 26 12:39:46 UTC 2020

    - v2.0 in PX4/Firmware (051bcf7): mavlink/c_library_v2@8f48168
    - v2.0 current upstream: mavlink/c_library_v2@5637057
    - Changes: mavlink/c_library_v2@8f48168...5637057

    5637057a 2020-12-23 PX4BuildBot - autogenerated headers for rev https://github.com/mavlink/mavlink/tree/b90bd6598c4a740ec8d8a7fddf4674b5a16f0489
5f03134f 2020-12-15 PX4BuildBot - autogenerated headers for rev https://github.com/mavlink/mavlink/tree/9aa844ab4256dbe526eaba77b7a03ca13cc5beda
9713e6a0 2020-12-11 PX4BuildBot - autogenerated headers for rev https://github.com/mavlink/mavlink/tree/710aab6d21b2769766bbbf8fe06388550e0963aa
7cdb26ad 2020-12-10 PX4BuildBot - autogenerated headers for rev https://github.com/mavlink/mavlink/tree/da7c444dcb9b71a928c3a8330a5e02b4d985c058
afc66162 2020-12-09 PX4BuildBot - autogenerated headers for rev https://github.com/mavlink/mavlink/tree/4e8f1de8d659e3ef910ecdc717daae550f9ed7f9