net: ipv6: Add IPv6 support to the ping socket.

This adds the ability to send ICMPv6 echo requests without a
raw socket. The equivalent ability for ICMPv4 was added in
2011.

Instead of having separate code paths for IPv4 and IPv6, make
most of the code in net/ipv4/ping.c dual-stack and only add a
few IPv6-specific bits (like the protocol definition) to a new
net/ipv6/ping.c. Hopefully this will reduce divergence and/or
duplication of bugs in the future.

Caveats:

- Setting options via ancillary data (e.g., using IPV6_PKTINFO
  to specify the outgoing interface) is not yet supported.
- There are no separate security settings for IPv4 and IPv6;
  everything is controlled by /proc/net/ipv4/ping_group_range.
- The proc interface does not yet display IPv6 ping sockets
  properly.

Tested with a patched copy of ping6 and using raw socket calls.
Compiles and works with all of CONFIG_IPV6={n,m,y}.

Signed-off-by: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/transp_v6.h b/include/net/transp_v6.h
index 938b7fd..eb40e71 100644
--- a/include/net/transp_v6.h
+++ b/include/net/transp_v6.h
@@ -11,6 +11,7 @@
 extern struct proto udpv6_prot;
 extern struct proto udplitev6_prot;
 extern struct proto tcpv6_prot;
+extern struct proto pingv6_prot;
 
 struct flowi6;
 
@@ -21,6 +22,8 @@
 extern void				ipv6_frag_exit(void);
 
 /* transport protocols */
+extern int				pingv6_init(void);
+extern void				pingv6_exit(void);
 extern int				rawv6_init(void);
 extern void				rawv6_exit(void);
 extern int				udpv6_init(void);