Load AGPS data for faster first fix

Getting a first fix seems to be at best slow at present. Not knowing that assistance loading might be implemented in ModemManager I tried it in a script which seems to improve first fix speed and reliability significantly. The down side is that, like the initial suggestion in #2, it requires ModemManager to be stopped to run it, then restarted afterwards. Due to the AT+QFUPL file upload needing the modem response before sending the file data I don't think it can be worked around with mmcli --command.

I've since realised ModemManager has a list of assistance server urls, and the file from one of these can be uploaded using nmcli -m0 --location-inject-assistance-data=xtra3grc.bin, but this doesn't seem to improve performance as the script above does. I'm probably missing a step.