The whole device breaks when the CPOL? query is sent; happening
consistently all the time:
<debug> [1626211395.825257] [modem4/ttyUSB3/at] --> 'AT+CPOL=,2<CR>'
<debug> [1626211395.842156] [modem4/ttyUSB3/at] <-- '<CR><LF>OK<CR><LF>'
<debug> [1626211395.843227] [modem4/sim4] loading preferred networks...
<debug> [1626211395.845289] [modem4/ttyUSB3/at] --> 'AT+CPOL?<CR>'
<debug> [1626211401.110974] [modem4/ttyUSB3/at] unexpected port hangup!
<debug> [1626211401.111586] [modem4/ttyUSB3/at] forced to close port
<debug> [1626211401.112331] [modem4/ttyUSB3/at] closing serial port...
<debug> [1626211401.112771] [modem4/ttyUSB3/at] serial port closed
Fixes https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/issues/401