QMI.WirelessData.start_network_interface

You're seeing just the function start_network_interface, go back to QMI.WirelessData module for more information.
Link to this function

start_network_interface(qmi, opts \\ [])

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Specs

Start the network interface

This will return once a packet data session is established and the interface can perform IP address configuration. That means once this returns you can configure the interface via DHCP.