dccp: fix info leak via getsockopt(DCCP_SOCKOPT_CCID_TX_INFO)

The CCID3 code fails to initialize the trailing padding bytes of struct
tfrc_tx_info added for alignment on 64 bit architectures. It that for
potentially leaks four bytes kernel stack via the getsockopt() syscall.
Add an explicit memset(0) before filling the structure to avoid the
info leak.

Signed-off-by: Mathias Krause <minipli@googlemail.com>
Cc: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>
static void ccid3_update_send_interval(struct ccid3_hc_tx_sock *hc)
{
	hc->tx_t_ipi = scaled_div32(((u64)hc->tx_s) << 6, hc->tx_x);

	DCCP_BUG_ON(hc->tx_t_ipi == 0);
	ccid3_pr_debug("t_ipi=%u, s=%u, X=%u\n", hc->tx_t_ipi,
		       hc->tx_s, (unsigned int)(hc->tx_x >> 6));
}

static void ccid3_update_send_interval(struct ccid3_hc_tx_sock *hc)
{
	hc->tx_t_ipi = scaled_div32(((u64)hc->tx_s) << 6, hc->tx_x);

	DCCP_BUG_ON(hc->tx_t_ipi == 0);
	ccid3_pr_debug("t_ipi=%u, s=%u, X=%u\n", hc->tx_t_ipi,
		       hc->tx_s, (unsigned int)(hc->tx_x >> 6));
}
