None of the new D-Bus interface cases use the bssid_part in
decompose_object_path (while the old interface ones do). As such, this
is dead code and can be removed. In addition, the P2P addition here was
pretty ugly extension. Replace these with a cleaner way of passing the
separating string (e.g., "Networks") from the caller and returning the
requested item.
In addition, there is no need to allocate the returned item separately,
so use a single allocation and a pointer to that allocated memory. This
will make it easier for callers to have to free only a single
allocation. This is also fixing a memory leak in P2P invitation
persistent group case where the caller had missed the need to free the
returned values.
Signed-off-by: Jouni Malinen <j@w1.fi>