AP_GPS: support GPSx_GNSS_MODE for F9P

[andyp1per]

This provides limited support for the GPSx_GNSS_MODE parameter. Specifically it allows you to turn off and on the SBAS. Galileo, Beidou and Glonass constellations. All signals for these constellations are left at the defaults. GPS and QZSS are left enabled as recommended and cannot be changed.

This PR also fixes 2 bugs in the UBLOX driver:

• Extensions are actually 30*N bytes for N extensions. Previously the buffer was sized too small meaning that extensions could be missed.
• 1 byte configuration items only use the LSB, so the other 7 bits need to masked out when checking that a configuration item is enabled or disabled

[andyp1per]

I have verified that all the allowed configurations work.

[MallikarjunSE]

Hey @andyp1per is it possible to look at F10N too? This module doesn't support GLONASS and sometimes very randomly I get GPS still configuring.

[andyp1per]

Hi @MallikarjunSE this work was sponsored by LightDyamix and I am done at this point. There are many enhancements that could be considered - including M10 support. Happy to look at this on a commercial basis, but I would need a sample as well to get it working. Cheers Andy

[tridge]

@MallikarjunSE I can test the F10N you sent me

[MallikarjunSE]

@MallikarjunSE I can test the F10N you sent me

Thanks @tridge