tcp: fix get_timewait4_sock() delay computation on 64bit

tcp: fix get_timewait4_sock() delay computation on 64bit

[ Upstream commit e2a1d3e47bb904082b758dec9d07edf241c45d05 ]

It seems I missed one change in get_timewait4_sock() to compute
the remaining time before deletion of IPV4 timewait socket.

This could result in wrong output in /proc/net/tcp for tm->when field.

Fixes: 96f817fedec4 ("tcp: shrink tcp6_timewait_sock by one cache line")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>