e2fsprogs: enable user namespace xattrs by default

User namespace xattrs are generally useful, and I think extN
is the only filesystem requiring a special mount option to
enable them, when xattrs are otherwise available.  So this
change sets that mount option into the defaults, via a
mke2fs.conf option.

Note that if xattrs are config'd off, this will lead to a
mostly-harmless:

   EXT4-fs (sdc1): (no)user_xattr options not supported

message at mount time...

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
diff --git a/lib/ext2fs/initialize.c b/lib/ext2fs/initialize.c
index 5e33173..cba2453 100644
--- a/lib/ext2fs/initialize.c
+++ b/lib/ext2fs/initialize.c
@@ -143,6 +143,7 @@
 	set_field(s_feature_compat, 0);
 	set_field(s_feature_incompat, 0);
 	set_field(s_feature_ro_compat, 0);
+	set_field(s_default_mount_opts, 0);
 	set_field(s_first_meta_bg, 0);
 	set_field(s_raid_stride, 0);		/* default stride size: 0 */
 	set_field(s_raid_stripe_width, 0);	/* default stripe width: 0 */