broadband-modem: generic Firehose and Sahara support
The Sahara and Firehose protocols are not specific to the Quectel plugin.
I've moved the renamed ID_MM_QUALCOMM_FIREHOSE
and ID_MM_QUALCOMM_SAHARA
environment variable check to broadband-modem
and chained up the parent's (broadband-modem's) load_update_settings
for all plugins having their custom update protocols.