[Reviewer: Andy] Improve HSS interop - use correct vendor IDs and fix host IP address

Andy,

Please can you review my fixes to the sdp library to improve HSS interop.  This fix comprises several changes.
- Don't include the Vendor-ID AVP at the top-level when reporting support for an application.
- Allow the product name and local IPv4 address to be configured.
- If we received a response with a vendor-specific application ID, still correlate it (don't just assume the vendor ID is 0).
- Avoid an exception when trying to trace out the application that we've just failed to find.

I've run the UT and live-tested against OpenIMS HSS, registering a subscriber and retrieving their configuration.

There are some corresponding crest changes to follow shortly.

Matt