Since we now have removed struct tipc_subscriber from the code, and
only struct tipc_subscription remains, there is no longer need for long
and awkward prefixes to distinguish between their pertaining functions.

We now change all tipc_subscrp_* prefixes to tipc_sub_*. This is
a purely cosmetic change.
Acked-by: NYing Xue <ying.xue@windriver.com>
Signed-off-by: NJon Maloy <jon.maloy@ericsson.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>