Correct manual section: "relayed traffic in shared networks"

The "Local and relayed traffic in shared networks" implies that using different "relay" values for different subnets within a shared network will cause the server to prefer the subnets with matching selector. In fact, the relay case is no different than selection via interface name (direct traffic). The server will initially select the subnet indicated by the relay, but will later change it to a subnet that was most recently used. The documentation must be corrected in that regard.