IPMX support?

[garethsb]

The VSF TR-10-x IPMX spec family defines some minor additions/modifications to the NMOS resources and SDP formats used for ST 2110.

Things I'm aware of...

• VSF_TR-10-1 requires an IPMX flag in the SDP format-specific parameters, measuredpixclk, vtotal and htotal for video and measuredsamplerate for audio
  • can these additions be handled entirely on the app-side, or are changes needed in nmos/sdp_utils.h? should be demo'd in nmos-cpp-node
• VSF TR-10-8 requires ext_link_offset_delay in the IS-05 Receiver transport parameters
  • can ext_ parameters be handled on the app-side or does this require changes in nmos/connection_api.cpp etc.? should be demo'd in nmos-cpp-node
• VSF TR-10-9 defines a default IPv4 multicast address scheme
  • can just be a simple utility function demo'd in nmos-cpp-node