Use a packet socket to receive packets.

Combined with the previous change to send on a raw socket
instead of a tunnel interface, this allows us to get rid of the
clat interface and remove all the routing configuration code.

(cherry picked from commit d44fac888a441cf21111358f43384f3942399d5d)

Bug: 15340961
Change-Id: I2147dbfc07321bbd64d3fb9762b1120487712133
9 files changed