xfce4-wavelan-plugin: Fix LICENSE format

* the COPYING file looks more like slightly modified BSD license and BenediktMeurer, FlorianRivoal
  are just names of Copyright holders, but I'll leave that to recipe maintainer
  fixes:
    WARNING: Recipe xfce4-wavelan-plugin, LICENSE (BenediktMeurer FlorianRivoal)
    has invalid format, LICENSES must have operator "([&|() ])" between them.

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>