Returns tunnel link status as sparse array-of-pairs grouped by status, replacing the dense N×N matrix from v1. The response contains linkInfo[status] = [[srcIndex, destIndex], ...] where each [srcIndex, destIndex] pair references indices into the nePks array. Status codes: 0=NO_TUNNEL, 1=UP, 2=PARTIALLY_DOWN, 3=DOWN, 4=NO_STATUS. Payload size is O(T) where T is the number of tunnel connections, compared to O(N²) in v1. No appliance count threshold — works at any scale. Supports ETag-based caching.