Create an IE item for the "Apparent Address" IE.

Also, don't initialize ie_item, in the hopes that cases where we don't
set it will be caught at compile time rather than run time.

Change-Id: I768251d19a7508ec876af44b987a4ecfd04258f7
Reviewed-on: https://code.wireshark.org/review/3759
Reviewed-by: Guy Harris <guy@alum.mit.edu>