[DCCP]: Twice the wrong reset code in receiving connection-Requests

[DCCP]: Twice the wrong reset code in receiving connection-Requests

This fixes two bugs in processing of connection-Requests in
v{4,6}_conn_request:

 1. Due to using the variable `reset_code', the Reset code generated
    internally by dccp_parse_options() is overwritten with the
    initialised value ("Too Busy") of reset_code, which is not what is
    intended.

 2. When receiving a connection-Request on a multicast or broadcast
    address, no Reset should be generated, to avoid storms of such
    packets. Instead of jumping to the `drop' label, the
    v{4,6}_conn_request functions now return 0. Below is why in my
    understanding this is correct:

    When the conn_request function returns < 0, then the caller,
    dccp_rcv_state_process(), returns 1. In all instances where
    dccp_rcv_state_process is called (dccp_v4_do_rcv, dccp_v6_do_rcv,
    and dccp_child_process), a return value of != 0 from
    dccp_rcv_state_process() means that a Reset is generated.

    If on the other hand the conn_request function returns 0, the
    packet is discarded and no Reset is generated.

Note: There may be a related problem when sending the Response, due to
the following.

	if (dccp_v6_send_response(sk, req, NULL))
		goto drop_and_free;
	/* ... */
	drop_and_free:
		return -1;

In this case, if send_response fails due to transmission errors, the
next thing that is generated is a Reset with a code "Too Busy". I
haven't been able to conjure up such a condition, but it might be good
to change the behaviour here also (not done by this patch).

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>