We need to add support for Source filtered multicasting aka (SSM) Source Specific Multicast.

This is a new model for multicasting which include the source
address as well as the destination multicast address in the specification
of multicast groups. This is effectively a subset of the existing
multicast model, in the sense that it restricts a multi-cast group
to a known set of sending addresses. This is a common use-case eg.
streaming apps, which by restricting the model solves a number
of problems with the general (any to any) model. These include:

1. The ability for any source to send to a m/c group leads to DoS issues
   with existing model.

2. multicast group addresses have meaning only within the scope
   of the senders which simplifies allocation (with SSM)

3. Simplified routing.

Probably requires a number of new methods/constructors on MulticastSocket to
specify sender addresses.