drivers/encx24j600: Implemented missing drop case
drivers/encx24j600: Implemented missing drop case

The netdev_driver_t::recv implementation of the encx24j600 does not provide the
drop feature. This commit adds it.

Fixes: #10410

x3ro/RIOT,yogo1212/RIOT,rfuentess/RIOT,mfrey/RIOT,authmillenon/RIOT,aeneby/RIOT,jasonatran/RIOT,basilfx/RIOT,aeneby/RIOT,basilfx/RIOT,josephnoir/RIOT,miri64/RIOT,cladmi/RIOT,smlng/RIOT,A-Paul/RIOT,authmillenon/RIOT,OlegHahm/RIOT,miri64/RIOT,toonst/RIOT,mfrey/RIOT,basilfx/RIOT,kYc0o/RIOT,jasonatran/RIOT,ant9000/RIOT,rfuentess/RIOT,yogo1212/RIOT,mfrey/RIOT,cladmi/RIOT,OlegHahm/RIOT,kaspar030/RIOT,x3ro/RIOT,A-Paul/RIOT,kYc0o/RIOT,mtausig/RIOT,x3ro/RIOT,OTAkeys/RIOT,lazytech-org/RIOT,josephnoir/RIOT,authmillenon/RIOT,authmillenon/RIOT,aeneby/RIOT,ant9000/RIOT,toonst/RIOT,miri64/RIOT,ant9000/RIOT,josephnoir/RIOT,yogo1212/RIOT,RIOT-OS/RIOT,mtausig/RIOT,mfrey/RIOT,kYc0o/RIOT,cladmi/RIOT,jasonatran/RIOT,authmillenon/RIOT,lazytech-org/RIOT,kYc0o/RIOT,smlng/RIOT,yogo1212/RIOT,toonst/RIOT,x3ro/RIOT,aeneby/RIOT,mtausig/RIOT,miri64/RIOT,RIOT-OS/RIOT,josephnoir/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,A-Paul/RIOT,mtausig/RIOT,jasonatran/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,toonst/RIOT,yogo1212/RIOT,josephnoir/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,OTAkeys/RIOT,toonst/RIOT,lazytech-org/RIOT,OlegHahm/RIOT,rfuentess/RIOT,rfuentess/RIOT,yogo1212/RIOT,miri64/RIOT,kaspar030/RIOT,OlegHahm/RIOT,kYc0o/RIOT,aeneby/RIOT,OlegHahm/RIOT,jasonatran/RIOT,basilfx/RIOT,lazytech-org/RIOT,rfuentess/RIOT,basilfx/RIOT,ant9000/RIOT,cladmi/RIOT,cladmi/RIOT,OTAkeys/RIOT,kaspar030/RIOT,x3ro/RIOT,authmillenon/RIOT,A-Paul/RIOT,A-Paul/RIOT,smlng/RIOT,ant9000/RIOT,mtausig/RIOT,mfrey/RIOT,smlng/RIOT,smlng/RIOT,lazytech-org/RIOT,kaspar030/RIOT