Use g_multi instead of g_serial to deliver Ethernet

debian/librem5-devkit-base.postinst

@@ -21,6 +21,8 @@ case "$1" in
     configure)
 	# Enable serial console over USB
 	systemctl enable serial-getty@ttyGS0
+	# Mass storage is required for Ethernet+serial over USB via g_multi
+	truncate -s 1M /var/lib/mass_storage_dummy
     ;;
 
     abort-upgrade|abort-remove|abort-deconfigure)

etc/modprobe.d/librem5-devkit.conf

+options g_multi file=/var/lib/mass_storage_dummy stall=0
 # Redpine WIFI module
 options rsi_91x dev_oper_mode=13 rsi_zone_enabled=1
 blacklist rsi_sdio

etc/modules-load.d/librem5-devkit.conf

-# Serial console over USB
-g_serial
+# Serial console and Ethernet over USB (plus dummy mass storage)
+g_multi