ipv6: enable anycast addresses as source addresses for datagrams

This change allows to consider an anycast address valid as source address
when given via an IPV6_PKTINFO or IPV6_2292PKTINFO ancillary data item.
So, when sending a datagram with ancillary data, the unicast and anycast
addresses are handled in the same way.

- Adds ipv6_chk_acast_addr_src() to check if an anycast address is link-local
  on given interface or is global.
- Uses it in ip6_datagram_send_ctl().

Signed-off-by: Francois-Xavier Le Bail <fx.lebail@yahoo.com>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/anycast.c

@@ -383,6 +383,17 @@ bool ipv6_chk_acast_addr(struct net *net, struct net_device *dev,
 	return found;
 }
 
+/*	check if this anycast address is link-local on given interface or
+ *	is global
+ */
+bool ipv6_chk_acast_addr_src(struct net *net, struct net_device *dev,
+			     const struct in6_addr *addr)
+{
+	return ipv6_chk_acast_addr(net,
+				   (ipv6_addr_type(addr) & IPV6_ADDR_LINKLOCAL ?
+				    dev : NULL),
+				   addr);
+}
 
 #ifdef CONFIG_PROC_FS
 struct ac6_iter_state {