Add address_to_bytes API.

Add address_to_bytes API.

This will copy an address's "byte format" into a buffer.  The original
intended design is for export_pdu functionality, which tries to do
this "manually" for many address types (and creates undesired dependencies)

The default functionality if a "byte format function" isn't provided
(currently the case for all address types) is a memcpy of the address
data.  Providing "address to byte" functions to aid export PDU
functionality will be provided later.

Change-Id: I3703f9e617a8cef09165ad53a0f98c6372676b9b
Reviewed-on: https://code.wireshark.org/review/16070
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Anders Broman <a.broman58@gmail.com>