ipv6_ext_rh: define RH type numbers at central place
ipv6_ext_rh: define RH type numbers at central place

This moves the type numbers for routing headers to a central place, as
we did it with other IANA-registered numbers.

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