syslog-ng: Fix build error

Add an upstream patch to fix the following build error.

  error: redefinition of typedef 'TransportMapperUnix'

Fixes:
http://autobuild.buildroot.net/results/c9b/c9b31d2de72a4e48a213b5c1d011814566732dfb



Signed-off-by: Chris Packham <judge.packham@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>