FEATURE_NOT_SUPPORTED is equal 1 in the enum FeatureSupport, as a
result even if QGPS isn't supported by modem debug message printed
available support.
ctx->supl is allocated in mm_shared_qmi_location_set_supl_server
using g_strdup. g_strdup requires to free string when unneeded.
The problem could be reproduced using following commands
```
while true; do
mmcli -m any --location-set-supl-server="supl.google.com:7276";
mem=$(cat /proc/$(pgrep ModemManager)/statm | awk '{print $6}')
echo $(date +"%s"), $mem | tee -a mm-leak.log;
done;
```
1) Not every allowed GSM7 character in UTF-8 incoding takes one
byte. Some (for example, 'à') take several bytes in input string, but
signle byte in GSM7.
2) Extended characters in GSM7 encoding take two bytes.
Otherwise for example sending following SMS fails:
```
mmcli -m a --messaging-create-sms="text='[wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww',number='+XXXXXXXXXXX'"
Successfully created new SMS: /org/freedesktop/ModemManager1/SMS/99
mmcli --send -s 99
error: couldn't send the SMS: 'GDBus.Error:org.freedesktop.libqmi.Error.Protocol.WmsEncoding: Couldn't write SMS part: QMI protocol error (58): 'WmsEncoding''
```
```
mmcli -m a --messaging-create-sms="text='|àààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààààà',number='+XXXXXXXXXXX'"
Successfully created new SMS: /org/freedesktop/ModemManager1/SMS/72
mmcli --send -s 72
error: couldn't send the SMS: 'GDBus.Error:org.freedesktop.ModemManager1.Error.Core.InvalidArgs: Couldn't convert UTF-8 to GSM: input UTF-8 validation failed'
```
Andrey Skvortsov