Add missing initrd config variables.

The `ZFS_INITRD_ADDITIONAL_DATASETS` variable is used in the initrd
script to boot additional OS file systems besides the root file system.
But it wasn't included as an example in the config files.

The `ZFS_POOL_EXCEPTIONS` *was* included in the example defaults file,
but it was not exported, so not available in the initrd.

Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Rob Norris <robn@despairlabs.com>
Signed-off-by: Turbo Fredriksson <turbo@bayour.com>
Closes #18000

etc/default/zfs.in

@@ -60,6 +60,10 @@ ZPOOL_IMPORT_ALL_VISIBLE='no'
 # This is a space separated list.
 #ZFS_POOL_EXCEPTIONS="test2"
 
+# Additional important (operating system) file systems to mount beside
+# the root file system.
+#ZFS_INITRD_ADDITIONAL_DATASETS="rpool/usr rpool/var rpool/var/spool"
+
 # Should the datasets be mounted verbosely?
 # A mount counter will be used when mounting if set to 'yes'.
 VERBOSE_MOUNT='no'

etc/zfs/zfs-functions.in

@@ -109,7 +109,7 @@ fi
 # ----------------------------------------------------
 
 export ZFS ZED ZPOOL ZPOOL_CACHE ZFS_LOAD_KEY ZFS_UNLOAD_KEY ZFS_MOUNT ZFS_UNMOUNT \
-    ZFS_SHARE ZFS_UNSHARE
+    ZFS_SHARE ZFS_UNSHARE ZFS_POOL_EXCEPTIONS ZFS_INITRD_ADDITIONAL_DATASETS
 
 zfs_action()
 {