Drop packets to the clat address.

These packets are not needed for 464xlat to function because
clatd reads packets from packet sockets, which run before
iptables, and the TC action also happens before packet sockets.

Their existence complicates data usage accounting, and in
certain situations results in applications receiving duplicate
UDP packets.

Bug: 65674744
Bug: 136193260
Test: atest netd_unit_test
Change-Id: I26bd8a1e7a54dbac86971b4e62f88f46ae5466f1