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/misc/mke2fs.conf.5.in b/misc/mke2fs.conf.5.in
index cb643eb..cb44c7f 100644
--- a/misc/mke2fs.conf.5.in
+++ b/misc/mke2fs.conf.5.in
@@ -314,6 +314,13 @@
 command-line option to
 .BR mke2fs (8).
 .TP
+.I default_mntopts
+This relation specifies the set of mount options which should be enabled
+by default.  These may be changed at a later time with the
+.B -o
+command-line option to
+.BR tune2fs (8).
+.TP
 .I blocksize
 This relation specifies the default blocksize if the user does not
 specify a blocksize on the command line.