main/linux-lts enable CONFIG_BLK_DEV_RBD
Currently only virt's rbd is enabled, but lts do not contain rbd module. This is quite common in k8s, ceph's environment.
$ grep CONFIG_BLK_DEV_RBD config-*
config-lts.aarch64:# CONFIG_BLK_DEV_RBD is not set
config-lts.armv7:# CONFIG_BLK_DEV_RBD is not set
config-lts.mips64:# CONFIG_BLK_DEV_RBD is not set
config-lts.ppc64le:# CONFIG_BLK_DEV_RBD is not set
config-lts.s390x:CONFIG_BLK_DEV_RBD=m
config-lts.x86:# CONFIG_BLK_DEV_RBD is not set
config-lts.x86_64:# CONFIG_BLK_DEV_RBD is not set
config-virt.aarch64:CONFIG_BLK_DEV_RBD=m
config-virt.armv7:CONFIG_BLK_DEV_RBD=m
config-virt.ppc64le:CONFIG_BLK_DEV_RBD=m
config-virt.x86:CONFIG_BLK_DEV_RBD=m
config-virt.x86_64:CONFIG_BLK_DEV_RBD=m