inet_diag: Cleanup type2proto last user

Now all the code works with sock_diag_req-compatible structs, so it's
possible to stop using the inet_diag_type2proto in inet_csk_diag_fill.
Pass the inet_diag_req into it and use the sdiag_protocol field. At the
same time remove the explicit ext argument, since it's also on the req.

However, this conversion is still required in _compat code, so just move
this routine, not remove.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: David S. Miller <davem@davemloft.net>