decnet: net/dn.h needs net/flow.h

Reported-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/dn.h

@@ -3,6 +3,7 @@
 
 #include <linux/dn.h>
 #include <net/sock.h>
+#include <net/flow.h>
 #include <asm/byteorder.h>
 #include <asm/unaligned.h>