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iface-modem-location: allow Cell ID only updates

Aleksander Morgado requested to merge aleksm/ModemManager:aleksander/allow-cid-only-updates into master

The "Serving System" indications reported via QMI when the device is moving may contain LAC/TAC+CID updates or just CID updates.

E.g. this one has "CID 3GPP" (0x1e):

  Mon Aug  3 11:22:42 2020 daemon.debug [1567]: [/dev/cdc-wdm0] received
  generic indication (translated)... <<<<<< QMUX: <<<<<<   length  = 33
  <<<<<<   flags   = 0x80 <<<<<<   service = "nas" <<<<<<   client  = 3
  <<<<<< QMI: <<<<<<   flags       = "indication" <<<<<<   transaction =
  4512 <<<<<<   tlv_length  = 21 <<<<<<   message     = "Serving System"
  (0x0024) <<<<<< TLV: <<<<<<   type       = "Serving System" (0x01)
  <<<<<<   length     = 6 <<<<<<   value      = 01:01:01:02:01:08 <<<<<<
    translated = [ registration_state = 'registered' cs_attach_state =
  'attached' ps_attach_state = 'attached' selected_network = '3gpp'
  radio_interfaces = '{ [0] = 'lte '}' ] <<<<<< TLV: <<<<<<   type
  = "Data Service Capability" (0x11) <<<<<<   length     = 2 <<<<<<
  value      = 01:0B <<<<<<   translated = { [0] = 'lte '} <<<<<< TLV:
  <<<<<<   type       = "CID 3GPP" (0x1e) <<<<<<   length     = 4 <<<<<<
    value      = 14:C2:A8:00 <<<<<<   translated = 11059732

And this one has both "CID 3GPP" (0x1e) and "LTE TAC" (0x25):

  Mon Aug  3 11:23:05 2020 daemon.debug [1567]: [/dev/cdc-wdm0] received
  generic indication (translated)... <<<<<< QMUX: <<<<<<   length  = 38
  <<<<<<   flags   = 0x80 <<<<<<   service = "nas" <<<<<<   client  = 3
  <<<<<< QMI: <<<<<<   flags       = "indication" <<<<<<   transaction =
  4513 <<<<<<   tlv_length  = 26 <<<<<<   message     = "Serving System"
  (0x0024) <<<<<< TLV: <<<<<<   type       = "Serving System" (0x01)
  <<<<<<   length     = 6 <<<<<<   value      = 01:01:01:02:01:08 <<<<<<
    translated = [ registration_state = 'registered' cs_attach_state =
  'attached' ps_attach_state = 'attached' selected_network = '3gpp'
  radio_interfaces = '{ [0] = 'lte '}' ] <<<<<< TLV: <<<<<<   type
  = "Data Service Capability" (0x11) <<<<<<   length     = 2 <<<<<<
  value      = 01:0B <<<<<<   translated = { [0] = 'lte '} <<<<<< TLV:
  <<<<<<   type       = "CID 3GPP" (0x1e) <<<<<<   length     = 4 <<<<<<
    value      = 32:36:BC:00 <<<<<<   translated = 12334642 <<<<<< TLV:
  <<<<<<   type       = "LTE TAC" (0x25) <<<<<<   length     = 2 <<<

We should therefore allow changes only in the CID, maintaining whatever LAC/TAC value we had before.

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