broadband-modem-qmi: Treat QMI_VOICE_USER_ACTION_UNKNOWN as QMI_VOICE_USER_ACTION_NOT_REQUIRED.
requested to merge dahopem/ModemManager:727_do_not_ignore_network-initiated_USSD-notify/mm-1-20 into mm-1-20
This fixes a bug where network-initiated USSD-Notify messages were not processed (and forwarded to higher-level applications) at all, while they should have been processed (and forwareded to higher-level applications). Previously, when there was a USSD conversation between the user and the network, the last message from the network (which, by definition, is not a message with user_action==QMI_VOICE_USER_ACTION_REQUIRED) would be silently dropped. The cause is a mismatch between the modem sending user_action==QMI_VOICE_USER_ACTION_UNKNOWN while old ModemManager expecting user_action==QMI_VOICE_USER_ACTION_NOT_REQUIRED.
This fixes #727 (closed) for the "mm-1-20" branch.