Add OSPF Area 0 support

[BarbarossaTM]

OSPFv2/v3 with Area 0 support only

[q3k]

I would like to see this implemented, too :)

Metallb might want to be able to talk OSPF soon, and being able to use bio-rd here would be wonderful (see: metallb/metallb#256).

[mraerino]

OSPFv3 packet handling PR is here: #225

[lwj5]

Just came across this issue from MetalLB as well. @BarbarossaTM any idea when #235 will be reviewed?