cc2538_rf: Add NETOPT_CHANNEL to getters
cc2538_rf: Add NETOPT_CHANNEL to getters

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