Add type for /system/bin/tcpdump.

We add this type with the intent to expose /system/bin/tcpdump to
vendor on userdebug devices only.

Bug: 111243627
Test: device boots /system/bin/tcpdump correctly labeled as
tcpdump_exec, can browse internet, turn wifi on/off
Change-Id: Icb35e84c87120d198fbb2b44edfa5edf6021d0f0