[NETLABEL]: Fix lookup logic of netlbl_domhsh_search_def.

Currently, if the call to netlbl_domhsh_search succeeds the
return result will still be NULL.

Fix that, by returning the found entry (if any).

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Acked-by: Paul Moore <paul.moore@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>