tipc: use negative error return values in functions

In some places, TIPC functions returns positive integers as return
codes. This goes against standard Linux coding practice, and may
even cause problems in some cases.

We now change the return values of the functions filter_rcv()
and filter_connect() to become signed integers, and return
negative error codes when needed. The codes we use in these
particular cases are still TIPC specific, since they are both
part of the TIPC API and have no correspondence in errno.h

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