examples/gcoap: add support for socket ZEP
examples/gcoap: add support for socket ZEP

miri64/RIOT,ant9000/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,ant9000/RIOT,miri64/RIOT,kaspar030/RIOT,authmillenon/RIOT,kYc0o/RIOT,jasonatran/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,jasonatran/RIOT,OTAkeys/RIOT,OTAkeys/RIOT,jasonatran/RIOT,ant9000/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,ant9000/RIOT,miri64/RIOT,OlegHahm/RIOT,kYc0o/RIOT,authmillenon/RIOT,kYc0o/RIOT,kaspar030/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,authmillenon/RIOT,authmillenon/RIOT,OTAkeys/RIOT,kaspar030/RIOT,kYc0o/RIOT,jasonatran/RIOT,ant9000/RIOT,kYc0o/RIOT,miri64/RIOT,authmillenon/RIOT,miri64/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,jasonatran/RIOT