Add clatd to apex/com.android.tethering-file_contexts

clatd binary is starting to be shipped by apex since T+ release
and the shipped clatd is belong to u:object_r:clatd_exec:s0.

Test: manual test
1. Connect to ipv6-only wifi.
2. Make IPv4 traffic.
   $ ping 8.8.8.8

Change-Id: I4f6f0944e94e165983a19a5d3c3a117274f6bbac
1 file changed