[DCCP]: Prepare the AF agnostic core for the introduction of DCCPv6

Basically exports a similar set of functions as the one exported by
the non-AF specific TCP code.

In the process moved some non-AF specific code from dccp_v4_connect to
dccp_connect_init and moved the checksum verification from
dccp_invalid_packet to dccp_v4_rcv, so as to use it in dccp_v6_rcv
too.

Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dccp/input.c

@@ -250,6 +250,8 @@ discard:
 	return 0;
 }
 
+EXPORT_SYMBOL_GPL(dccp_rcv_established);
+
 static int dccp_rcv_request_sent_state_process(struct sock *sk,
 					       struct sk_buff *skb,
 					       const struct dccp_hdr *dh,
@@ -567,3 +569,5 @@ discard:
 	}
 	return 0;
 }
+
+EXPORT_SYMBOL_GPL(dccp_rcv_state_process);