linux-yocto: enable BLK_DEV_NBD as preparation for streaming support

The upcoming release of RAUC will come with built-in HTTP streaming
support. This requires BLK_DEV_NBD to be present in the kernel.
By default, this is currently compiled as a module but we do not ensure
this yet and it is simpler to have it compiled-in.

Signed-off-by: Enrico Jorns <ejo@pengutronix.de>

recipes-kernel/linux/linux-yocto/rauc.cfg

@@ -2,5 +2,6 @@ CONFIG_BLK_DEV_LOOP=y
 CONFIG_SQUASHFS=y
 CONFIG_MD=y
 CONFIG_BLK_DEV_DM=y
+CONFIG_BLK_DEV_NBD=y
 CONFIG_DM_VERITY=y
 CONFIG_CRYPTO_SHA256=y