In short:
* The 'sierra-legacy' plugin will handle all the old AT based modems,
including the DirectIP ones. This plugin is filtered by driver ('sierra' or
'sierra_net') and forbidden-drivers ('qmi_wwan' and 'cdc_mbim'). This plugin
should also grab HP and AT&T branded models if they are handled by the
proper kernel driver.
* The 'sierra' plugin will only handle QMI or MBIM based Sierra modems, which
are really all the new ones. This plugin is filtered by VID (0x1199) and
driver (qmi_wwan and cdc_mbim).
For this separation to work, the 'sierra' and 'sierra_net' plugins need to be
complementary to each other.