ipv6: Nonlocal bind

Add support to allow non-local binds similar to how this was done for IPv4.
Non-local binds are very useful in emulating the Internet in a box, etc.

This add the ip_nonlocal_bind sysctl under ipv6.

Testing:

Set up nonlocal binding and receive routing on a host, e.g.:

ip -6 rule add from ::/0 iif eth0 lookup 200
ip -6 route add local 2001:0:0:1::/64 dev lo proto kernel scope host table 200
sysctl -w net.ipv6.ip_nonlocal_bind=1

Set up routing to 2001:0:0:1::/64 on peer to go to first host

ping6 -I 2001:0:0:1::1 peer-address -- to verify

Signed-off-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/ping.c b/net/ipv4/ping.c
index 05ff44b..e89094a 100644
--- a/net/ipv4/ping.c
+++ b/net/ipv4/ping.c
@@ -363,7 +363,8 @@
 						    scoped);
 		rcu_read_unlock();
 
-		if (!(isk->freebind || isk->transparent || has_addr ||
+		if (!(net->ipv6.sysctl.ip_nonlocal_bind ||
+		      isk->freebind || isk->transparent || has_addr ||
 		      addr_type == IPV6_ADDR_ANY))
 			return -EADDRNOTAVAIL;