linux-yocto/5.15: cfg: fix DECNET configuration warning

-stable merged the DECNET removal to 5.15, so we integrate
the following kernel-cache commit to fix the kernel configuration
audit warning:

    b647d9611cb base: drop CONFIG_DECNET

Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>
(cherry picked from commit 06ef70ac)
Signed-off-by: Steve Sakoman <steve@sakoman.com>