Add ShellCheck's --enable=all inside cmd/

The only exception is `cmd/vdev_id/vdev_id` which might be a subject of
refactoring (see #12084)

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Signed-off-by: szubersk <szuberskidamian@gmail.com>
Closes #12912

cmd/zpool/zpool.d/lsblk

@@ -66,6 +66,7 @@ for i in $list ; do
 
 	# Special case: Looking up the size of a file-based vdev can't
 	# be done with lsblk.
+	# shellcheck disable=SC2154
 	if [ "$i" = "size" ] && [ -f "$VDEV_UPATH" ] ; then
 		size=$(du -h --apparent-size "$VDEV_UPATH" | cut -f 1)
 		echo "size=$size"