package/netatalk: security bump to version 3.1.23

package/netatalk: security bump to version 3.1.23

Fixes CVE-2018-1160: Netatalk before 3.1.12 is vulnerable to an out of
bounds write in dsi_opensess.c.  This is due to lack of bounds checking on
attacker controlled data.  A remote unauthenticated attacker can leverage
this vulnerability to achieve arbitrary code execution.

For more details, see the release notes:
http://netatalk.sourceforge.net/3.1/ReleaseNotes3.1.12.html

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>