[nd6] add RaFlagsExtOption and track flags in received RAs (#9448)
#1417
| Job | Run time |
|---|---|
| 40m 37s | |
| 5m 10s | |
| 4m 40s | |
| 6m 48s | |
| 5m 5s | |
| 15m 29s | |
| 8m 41s | |
| 35s | |
| 14s | |
| 1h 27m 19s |