[INET_SOCK]: Move struct inet_sock & helper functions to net/inet_sock.h

To help in reducing the number of include dependencies, several files were
touched as they were getting needed headers indirectly for stuff they use.

Thanks also to Alan Menegotto for pointing out that net/dccp/proto.c had
linux/dccp.h include twice.

Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index 11a7256..860bbac 100644
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -541,6 +541,9 @@
 extern const struct proto_ops inet6_stream_ops;
 extern const struct proto_ops inet6_dgram_ops;
 
+struct group_source_req;
+struct group_filter;
+
 extern int ip6_mc_source(int add, int omode, struct sock *sk,
 			 struct group_source_req *pgsr);
 extern int ip6_mc_msfilter(struct sock *sk, struct group_filter *gsf);