The failure is caused by a RA packet read race condition. The test
receives a callback that local-only tethering has started and
immediately begins listening for an RA. However, the system's RA daemon
may not have finished initializing.
The test's packet reader times out waiting for an RA and returns a null
packet. The waitForRouterAdvertisement then uses the null packet
checking for RA, causing NPE. Change modifies waitForRouterAdvertisement
to check if a packet is null before processing it.
Flag: EXEMPT bugfix
Bug: 418010532
Test: atest android.net.EthernetTetheringTest#testLocalOnlyTethering
Change-Id: Ic534c53766958ae48a82687a9bd6d09297f074f2
6fecb23808