I managed to get the WiFi and the MCU onto the same local area network by changing usbnet config to 3 and restarting the device as per this post and enabling CONFIG_USB_NET_RNDIS_HOST in the kernel. I think I also had to make this change to the kernel for /dev/ttyUSB2 to continue to respond to AT commands.
However, I now have a new problem. quectelCM seems to have stopped working so MCU is now unable to access the internet. This is the execution log:
[root@rk3399:~]# quectelCM
[12-21_08:55:34:273] WCDMA<E_QConnectManager_Linux&Android_V1.1.45
[12-21_08:55:34:273] quectelCM profile[1] = (null)/(null)/(null)/0, pincode = (null)
[12-21_08:55:34:274] Find /sys/bus/usb/devices/3-1.2 idVendor=2c7c idProduct=0125
[12-21_08:55:34:274] Find /sys/bus/usb/devices/3-1.2:1.4/net/usb1
[12-21_08:55:34:274] Find usbnet_adapter = usb1
[12-21_08:55:34:274] Find /sys/bus/usb/devices/3-1.2:1.4/GobiQMI/qcqmi1
[12-21_08:55:34:274] Find qmichannel = /dev/qcqmi1
[12-21_08:55:34:282] failed to get ClientID for 0x01 errno: 32 (Broken pipe)
[12-21_08:55:34:282] Get clientWDS = 0
[12-21_08:55:34:283] failed to get ClientID for 0x02 errno: 32 (Broken pipe)
[12-21_08:55:34:283] Get clientDMS = 0
[12-21_08:55:34:284] failed to get ClientID for 0x03 errno: 32 (Broken pipe)
[12-21_08:55:34:284] Get clientNAS = 0
[12-21_08:55:34:285] failed to get ClientID for 0x0b errno: 32 (Broken pipe)
[12-21_08:55:34:285] Get clientUIM = 0
[12-21_08:55:34:288] failed to get ClientID for 0x1a errno: 32 (Broken pipe)
[12-21_08:55:34:288] Get clientWDA = 0
[12-21_08:55:34:288] GobiNetThread Failed to open /dev/qcqmi1, errno: 32 (Broken pipe)
[12-21_08:55:34:288] main Failed to init QMIThread: 22 (Invalid argument)
Verify that qcqmi1 is being created:
[root@rk3399:~]# dmesg | grep qcqmi
[ 2.430925] creating qcqmi1
[root@rk3399:~]# ls -lah /dev/qcqmi1
crw------- 1 root root 240, 0 Dec 21 08:40 /dev/qcqmi1