tipc: remove redundant timer defined in tipc_sock struct

Remove the redundant timer defined in tipc_sock structure, instead we
can directly reuse the sk_timer defined in sock structure.

Signed-off-by: Ying Xue <ying.xue@windriver.com>
Acked-by: Erik Hugne <erik.hugne@ericsson.com>
Reviewed-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>