net neighbour, decnet: Ensure to align device private data on preferred alignment.

To allow both of protocol-specific data and device-specific data
attached with neighbour entry, and to eliminate size calculation
cost when allocating entry, sizeof protocol-speicic data must be
multiple of NEIGH_PRIV_ALIGN.  On 64bit archs,
sizeof(struct dn_neigh) is multiple of NEIGH_PRIV_ALIGN, but on
32bit archs, it was not.

Introduce NEIGH_ENTRY_SPACE() macro to ensure that protocol-specific
entry-size meets our requirement.

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index 629ee57..7e748ad 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -181,6 +181,7 @@
 };
 
 #define NEIGH_PRIV_ALIGN	sizeof(long long)
+#define NEIGH_ENTRY_SIZE(size)	ALIGN((size), NEIGH_PRIV_ALIGN)
 
 static inline void *neighbour_priv(const struct neighbour *n)
 {