tipc: Eliminate improper use of TIPC_OK error code

This patch corrects many places where TIPC routines indicated
successful completion by returning TIPC_OK instead of 0.
(The TIPC_OK symbol has the value 0, but it should only be used
in contexts that deal with the error code field of a TIPC
message header.)

Signed-off-by: Allan Stephens <allan.stephens@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>