ipv6: 64bit version of ipv6_addr_set().

index 77cef332..fb7f7c6 100644
@@ -355,14 +355,32 @@ static inline void ipv6_addr_prefix(struct in6_addr *pfx,
 		pfx->s6_addr[o] = addr->s6_addr[o] & (0xff00 >> b);
 }
 
+static inline void __ipv6_addr_set_half(__be32 *addr,
+					__be32 wh, __be32 wl)
+{
+#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) && BITS_PER_LONG == 64
+#if defined(__BIG_ENDIAN)
+	if (__builtin_constant_p(wh) && __builtin_constant_p(wl)) {
+		*(__force u64 *)addr = ((__force u64)(wh) << 32 | (__force u64)(wl));
+		return;
+	}
+#elif defined(__LITTLE_ENDIAN)
+	if (__builtin_constant_p(wl) && __builtin_constant_p(wh)) {
+		*(__force u64 *)addr = ((__force u64)(wl) << 32 | (__force u64)(wh));
+		return;
+	}
+#endif
+#endif
+	addr[0] = wh;
+	addr[1] = wl;
+}
+
 static inline void ipv6_addr_set(struct in6_addr *addr, 
 				     __be32 w1, __be32 w2,
 				     __be32 w3, __be32 w4)
 {
-	addr->s6_addr32[0] = w1;
-	addr->s6_addr32[1] = w2;
-	addr->s6_addr32[2] = w3;
-	addr->s6_addr32[3] = w4;
+	__ipv6_addr_set_half(&addr->s6_addr32[0], w1, w2);
+	__ipv6_addr_set_half(&addr->s6_addr32[2], w3, w4);
 }
 
 static inline bool ipv6_addr_equal(const struct in6_addr *a1,