Drop the unsolicited multicast NA to all routers address in APF.

Send the unsolicited multicast NA after roaming proactively to IPv6 all
routers address(ff02::2), to improve the NUD(Neighbor Unreachability
Detection) failure cases. For power saving purpose, drop the multicast
NA packet to all routers address as well.

Bug: 80379409
Bug: 162944199
Test: atest android.net.apf.ApfTest
Change-Id: I7867110b3cbfc217055e38f08d172c9208e05486