🐛 Graft only connections on attach_shmdata

When attaching a shmdata to a SIP buddy, graft only the relevant part of the buddy's tree (.buddies.<id>.connections) instead of the whole buddy tree. This is something that would be very useful for Scenic devs.

The logic for detaching a shmdata from a SIP buddy already works like this, it grafts only the relevant part of the tree instead of the whole tree. This fix would actually make sure that both functions work similarly.