images: squashfs: xattrs should not depend on buld host

Enable xattr for the generated squashfs only if needed for SELinux.
This eliminates warnings during boot on target when building
(non-SELinux) OpenWrt on SELinux-enabled hosts like Fedora.

Reported-by: fda77 <fda77@users.noreply.github.com>
Signed-off-by: Daniel Golle <daniel@makrotopia.org>

include/image.mk

@@ -75,6 +75,7 @@ JFFS2OPTS += $(MKFS_DEVTABLE_OPT)
 SQUASHFS_BLOCKSIZE := $(CONFIG_TARGET_SQUASHFS_BLOCK_SIZE)k
 SQUASHFSOPT := -b $(SQUASHFS_BLOCKSIZE)
 SQUASHFSOPT += -p '/dev d 755 0 0' -p '/dev/console c 600 0 0 5 1'
+SQUASHFSOPT += $(if $(CONFIG_SELINUX),-xattr,-no-xattrs)
 SQUASHFSCOMP := gzip
 LZMA_XZ_OPTIONS := -Xpreset 9 -Xe -Xlc 0 -Xlp 2 -Xpb 2
 ifeq ($(CONFIG_SQUASHFS_XZ),y)