Restore tcpdump.

tcpdump accidentally fell off the device when its Android.mk was converted
to Android.bp.

Bug: http://b/111654811
Test: builds
Change-Id: Ia49a6722b47c9017b6e573cb88f7a93f3d95db5d
diff --git a/shell_and_utilities/Android.bp b/shell_and_utilities/Android.bp
index 7834dd5..0586381 100644
--- a/shell_and_utilities/Android.bp
+++ b/shell_and_utilities/Android.bp
@@ -18,6 +18,7 @@
         "newfs_msdos",
         "reboot",
         "sh",
+        "tcpdump",
         "toolbox",
         "toybox",
     ],