[NET]: Change "not found" return value for rule lookup

This changes the "not found" error return for the lookup
function to -ESRCH so that it can be distinguished from
the case where a rule or route resulting in -ENETUNREACH
has been found during the search.

It fixes a bug where if DECnet was compiled with routing
support, but no routes were added to the routing table,
it was failing to fall back to endnode routing.
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: Patrick Caulfield <pcaulfie@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/fib_rules.c

@@ -143,7 +143,7 @@ int fib_rules_lookup(struct fib_rules_ops *ops, struct flowi *fl,
 		}
 	}
 
-	err = -ENETUNREACH;
+	err = -ESRCH;
 out:
 	rcu_read_unlock();