lxd/storage/drivers/zfs: change posixacl to equivalent posix

Using `posixacl` as an alias to `posix` (as can be seen here
https://openzfs.github.io/openzfs-docs/man/master/7/zfsprops.7.html#acltype)
leads to `filterRedundantOptions` not filtering out `acltype=posixacl` when comparing it to the current setting `posix`.

Signed-off-by: hamistao <pedro.ribeiro@canonical.com>

lxd/storage/drivers/driver_zfs.go

@@ -34,7 +34,7 @@ var zfsDefaultSettings = map[string]string{
 	"setuid":     "on",
 	"exec":       "on",
 	"devices":    "on",
-	"acltype":    "posixacl",
+	"acltype":    "posix", // acltype "posix" is equivalent to "posixacl". Set as "posix" to avoid setting it multiple times on ensureInitialDatasets.
 	"xattr":      "sa",
 }