You should be able to unlock it flashing this in TWRP.
Inviato dal mio ONEPLUS A5010 utilizzando Tapatalk
This should be the link for LTE ROW version
This should be the link for the full OOS 4.7.4
I see that the Marshmallow OTA link is available, eg here:
However, I'm not sure I understand how that relates to your kernel. Could I update to that OTA and use ...
I have a new problem at the booting TWRP stage:
C:\shield>fastboot boot twrp-multirom-20151112-UNOFFICIAL-foster.img
OKAY < 0.831s>