[DCCP]: Remove redundant statements in init_sequence (ISS)

This patch removes the following redundancies:

 1) The test skb->protocol == htons(ETH_P_IPV6) in dccp_v6_init_sequence
    is always true since
     * dccp_v6_conn_request() is the only calling function
     * dccp_v6_conn_request() redirects all skb's with ETH_P_IP to
       dccp_v4_conn_request()

 2) The first argument, `struct sock *sk', of dccp_v{4,6}_init_sequence()
    is never used.

(This is similar for tcp_v{4,6}_init_sequence, an analogous patch has been
 submitted to netdev and merged.)

By the way - are the `sport' / `dport' arguments in the right order?
I have made them consistent among calls but they seem to be in the
reverse order.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>