zink: make ZINK_DESCRIPTOR_MODE=db the default
this has been getting beat up a lot lately by radv ci (and me), so it should be ready to turn on by default for even more testing in advance of the 23.1 release
this has been getting beat up a lot lately by radv ci (and me), so it should be ready to turn on by default for even more testing in advance of the 23.1 release