modemmanager: skip virtual net devices in hotplug script

modemmanager: skip virtual net devices in hotplug script

Every net uevent - eth ports, USB hubs, bridges, taps, SQM IFB,
GRE tunnels, veth, tun/tap - is handed to mmcli via
25-modemmanager-net's mm_report_event call, so ModemManager logs a
'not supported by any plugin' notice per device on every boot and
hotplug replay:

  ModemManager[15132]: <msg> [base-manager] couldn't check support
    for device '.../fsl-ehci.0/usb1/1-1/1-1.1':
    not supported by any plugin

mm_report_event() already discards virtual devices internally, but
only after mm_log "info" has written a "hotplug: add network
interface XXX: event processed" line to daemon.info for every one
of them.

Mirror the same guard in the hotplug script by exiting early when
DEVPATH points under /devices/virtual/*, which covers SQM IFB, GRE,
bridges, veth, tun/tap.  This never rejects a physical modem port
(kernel wwan, MHI, USB CDC/RNDIS/QMI/MBIM are all under real bus
subtrees).

Signed-off-by: Michael Pfeifroth <redacted>