gnrc_netif: add send function
gnrc_netif: add send function

authmillenon/RIOT,miri64/RIOT,yogo1212/RIOT,jasonatran/RIOT,authmillenon/RIOT,kYc0o/RIOT,OlegHahm/RIOT,smlng/RIOT,yogo1212/RIOT,basilfx/RIOT,jasonatran/RIOT,authmillenon/RIOT,ant9000/RIOT,yogo1212/RIOT,smlng/RIOT,ant9000/RIOT,miri64/RIOT,basilfx/RIOT,smlng/RIOT,kYc0o/RIOT,kaspar030/RIOT,smlng/RIOT,RIOT-OS/RIOT,basilfx/RIOT,kaspar030/RIOT,kaspar030/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,miri64/RIOT,yogo1212/RIOT,kaspar030/RIOT,kYc0o/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,kaspar030/RIOT,yogo1212/RIOT,OTAkeys/RIOT,ant9000/RIOT,kYc0o/RIOT,jasonatran/RIOT,authmillenon/RIOT,jasonatran/RIOT,OTAkeys/RIOT,basilfx/RIOT,basilfx/RIOT,jasonatran/RIOT,OlegHahm/RIOT,yogo1212/RIOT,ant9000/RIOT,miri64/RIOT,RIOT-OS/RIOT,miri64/RIOT,OTAkeys/RIOT,OTAkeys/RIOT,ant9000/RIOT,smlng/RIOT