implement ClatdController::dumpEgress()

combined with later commits that populate the map this results in:

$ echo; adb shell dumpsys netd | sed -rn '/^  ClatdController$/,/^$/p'

  ClatdController
    Trackers: iif[iface] nat64Prefix v6Addr -> v4Addr v4iif[v4iface] [netId]
      11[rmnet_data1] 2607:7700:0:1c:0:1::/96 2607:fb90:270a:a0c7:86e7:29f:b165:fe89 -> 192.0.0.4 33[v4-rmnet_data1] [100]
      30[wlan0] 64:ff9b::/96 2401:fa00:480:13d:ca58:52b2:68ee:164d -> 192.0.0.5 34[v4-wlan0] [102]
    BPF ingress map: iif(iface) nat64Prefix v6Addr -> v4Addr oif(iface)
      30(wlan0) 64:ff9b::/96 2401:fa00:480:13d:ca58:52b2:68ee:164d -> 192.0.0.5 34(v4-wlan0)
      11(rmnet_data1) 2607:7700:0:1c:0:1::/96 2607:fb90:270a:a0c7:86e7:29f:b165:fe89 -> 192.0.0.4 33(v4-rmnet_data1)
    BPF egress map: iif(iface) v4Addr -> v6Addr nat64Prefix oif(iface)
      34(v4-wlan0) 192.0.0.5 -> 2401:fa00:480:13d:ca58:52b2:68ee:164d 64:ff9b::/96 30(wlan0)
      33(v4-rmnet_data1) 192.0.0.4 -> 2607:fb90:270a:a0c7:86e7:29f:b165:fe89 2607:7700:0:1c:0:1::/96 11(rmnet_data1)

Test: compiles, atest, flashed to a device and ran dumpsys netd (see above)
Bug: 139396664
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I802554463d78cad7fe8d289ae5f0c1730384894c