Interfaces to abstract subnets may not be needed

[mike1813]

Pattern ILSA+c adds a relationship from a host to logical subnet interface to any abstract subnet for which the logical subnet provides part of the implementation.

This means a host connected to (say) a cellular access network would have an interface to the access network but this interface would also be related to the cellular network.

In most other places, we assume the host is not really connected to the abstract network, and therefore no interface should need to exist between the host and the abstract network. So it is unclear why pattern ILSA+c would be needed. This should be investigated, and ideally this pattern should be removed.