broadband-modem-qmi: retry when "Get Serving System" fails
Sometimes the modem is not ready and answers "FAILURE: InformationUnavailable". Rather than failing permanently, modem manager should retry until the modem is ready.
fixes #667
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Sometimes the modem is not ready and answers "FAILURE: InformationUnavailable". Rather than failing permanently, modem manager should retry until the modem is ready.
fixes #667