tipc: do not report -EHOSTUNREACH for failed local delivery

tipc: do not report -EHOSTUNREACH for failed local delivery

Since commit 1186adf7df04 ("tipc: simplify message forwarding and
rejection in socket layer") -EHOSTUNREACH is propagated back to
the sending process if we fail to deliver the message to another
socket local to the node.
This is wrong, host unreachable should only be reported when the
destination port/name does not exist in the cluster, and that
check is always done before sending the message. Also, this
introduces inconsistent sendmsg() behavior for local/remote
destinations. Errors occurring on the receiving side should not
trickle up to the sender. If message delivery fails TIPC should
either discard the packet or reject it back to the sender based
on the destination droppable option.

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