mm/util: make strndup_user description a kernel-doc comment

mm/util: make strndup_user description a kernel-doc comment

Patch series "memory management documentation updates", v3.

Here are several updates to the mm documentation.

Aside from really minor changes in the first three patches, the updates
are:

* move the documentation of kstrdup and friends to "String Manipulation"
  section
* split memory management API into a separate .rst file
* adjust formating of the GFP flags description and include it in the
  reference documentation.

This patch (of 7):

The description of the strndup_user function misses '*' character at the
beginning of the comment to be proper kernel-doc.  Add the missing
character.

Link: http://lkml.kernel.org/r/1532626360-16650-2-git-send-email-rppt@linux.vnet.ibm.com
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>