Cannot configure multi-GNSS for ZED F9P

[TheExplorer95]

Describe the bug
Configuration of the F9P to use any other GNSS system besides GPS results in a 'UBX-ACK-NAK' error message.

To Reproduce

1. Checkout 'master'
2. Configure the ublox package to use this config zed_f9p-nmea.txt (unfortunately github does not support yaml extension, I've changed it to .txt which has to be changed to yaml before initialization)
3. Make sure the F9P receiver is connected to /dev/ttyACM0 or adapt the config file to your needs.
4. Launch the ublox node and receive the following error msg when e.g. :
   Example output with gnss/glonass: true, which has been set in the provided F9P config
   

Expected behavior
One of both would be appreciated (for more information see link chapter: 5.9.8.1 GNSS system configuration):

• The configuration of multiple GNSS systems for the F9P should work based on the current approach (needs to be adjusted to UBX-CFGVALSET, UBX-CFG-VALGET, UBX-CFG-VALDEL)
• The configuration of multiple GNSS systems for the F9P should be adjusted to use CFG-SIGNAL-???

Desktop:

• OS: Ubuntu 20.04
• ROS Version: ROS1 Noetic

Additional context
I'm working on a project using the C099-F9P board to localize a robot. So far I was able to set up the NMEA/RTCM messages in ROS. The communication with the ntrip client works fine and I'm able to acquire float-RTK. I want to further increase the accuracy with additional satellite sources, currently I'm achieving 127mm hacc and 165mm vacc.