+CTZU URCs not processed
Testing on a Cinterion PLS8, I see we're not handling +CTZU URCs:
ModemManager[26693]: <debug> [1562665926.726303] (ttyACM1): <-- '<CR><LF>+CTZU: "19/07/09,09:52:06",+08,1<CR><LF><CR><LF>'
ModemManager[26693]: <debug> [1562665944.031016] loading signal quality...
ModemManager[26693]: <debug> [1562665944.031703] (ttyACM1) device open count is 2 (open)
ModemManager[26693]: <debug> [1562665944.032603] (ttyACM1): --> 'AT+CIND?<CR>'
ModemManager[26693]: <debug> [1562665944.059004] (ttyACM1): <-- '<CR><LF>+CIND: 0,2,1,1,0,1,1,0<CR><LF><CR><LF>OK<CR><LF>'
ModemManager[26693]: <debug> [1562665944.062069] (ttyACM1) Could not parse CIND signal quality results: Could not parse the +CIND response '+CTZU: "19/07/09,09:52:06",+08,1
+CIND: 0,2,1,1,0,1,1,0': no CIND tag found