Convert socket (port) listing to compat dumpit call. If a socket
(port) has publications a second dumpit call is issued to collect them
and format then into the legacy buffer before continuing to process
the sockets (ports).

Command converted in this patch:
TIPC_CMD_SHOW_PORTS
Signed-off-by: NRichard Alpe <richard.alpe@ericsson.com>
Reviewed-by: NErik Hugne <erik.hugne@ericsson.com>
Reviewed-by: NYing Xue <ying.xue@windriver.com>
Reviewed-by: NJon Maloy <jon.maloy@ericsson.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>