open-lldp: add patch to remove -Werror

-Werror causes a number of build failures with recent versions of gcc
 that have additional warnings (turned into error due to -Werror). So
 let's remove -Werror.

Fixes:

  http://autobuild.buildroot.net/results/a06feb8616b98d4931145ea5079650e06bd1a61d/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>