ZFS package not compiling on recent kernel

Installing `zfs` results in the following errors:

```

In file included from /tmp/guix-build-zfs-0.8.5.drv-0/zfs-0.8.5/include/sys/dmu.h:848:0,

from /tmp/guix-build-zfs-0.8.5.drv-0/zfs-0.8.5/include/sys/spa.h:44,

from /tmp/guix-build-zfs-0.8.5.drv-0/zfs-0.8.5/include/sys/spa_impl.h:35,

from /tmp/guix-build-zfs-0.8.5.drv-0/zfs-0.8.5/module/zfs/vdev_disk.c:30:

/tmp/guix-build-zfs-0.8.5.drv-0/zfs-0.8.5/module/zfs/vdev_disk.c: In function 'vdev_disk_open':

/tmp/guix-build-zfs-0.8.5.drv-0/zfs-0.8.5/include/linux/blkdev_compat.h:378:37: error: implicit declaration of function 'check_disk_change'; did you mean 'bdev_disk_changed'? [-Werror=implicit-function-declaration]

#define vdev_bdev_reread_part(bdev) check_disk_change(bdev)

^

/tmp/guix-build-zfs-0.8.5.drv-0/zfs-0.8.5/module/zfs/vdev_disk.c:218:17: note: in expansion of macro 'vdev_bdev_reread_part'

int error = vdev_bdev_reread_part(bdev);

^~~~~~~~~~~~~~~~~~~~~

/tmp/guix-build-zfs-0.8.5.drv-0/zfs-0.8.5/module/zfs/vdev_disk.c: In function 'vdev_blkg_tryget':

/tmp/guix-build-zfs-0.8.5.drv-0/zfs-0.8.5/module/zfs/vdev_disk.c:506:37: error: 'struct percpu_ref' has no member named 'count'

rc = atomic_long_inc_not_zero(&ref->count);

^~

cc1: some warnings being treated as errors

```

This is using kernel 5.10.2 I believe:

```

downloading from https://ci.guix.gnu.org/nar/lzip/si6ly6im9ih9fpycp5zq1895y2jl4kzm-linux-libre-5.10.2...

linux-libre-5.10.2 76.4MiB

downloading from https://ci.guix.gnu.org/nar/lzip/gw4nybiqbfg7mayvykvrk4vd7jf2liyx-linux-libre-module-builder-5.10.2...

linux-libre-module-builder-5.10.2 17.4MiB

```

Looking at recent zfs release note: https://github.com/openzfs/zfs/releases/tag/zfs-0.8.5and https://github.com/openzfs/zfs/releases/tag/zfs-0.8.6

zfs-0.8.6 includes a few "Linux 5.10 compat" but is still not rated for 5.10.

Would it be possible to fix this by adding `#:linux ,linux-libre-5.9` to the `arguments` field of the `zfs` package?

Of course, it does require that we use a specific linux version.

Looking at recent zfs release note: https://github.com/openzfs/zfs/releases/tag/zfs-0.8.5and https://github.com/openzfs/zfs/releases/tag/zfs-0.8.6

zfs-0.8.6 includes a few "Linux 5.10 compat" but is still not rated for 5.10.

Would it be possible to fix this by adding `#:linux ,linux-libre-5.9` to the `arguments` field of the `zfs` package?

Of course, it does require that we use a specific linux version.