In preparation for unconditionally passing the struct timer_list pointer to
all timer callbacks, switch to using an explicit static variable to hold
additional expiration details.

Cc: "David S. Miller" <davem@davemloft.net>
Cc: Bhumika Goyal <bhumirks@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: "Reshetova, Elena" <elena.reshetova@intel.com>
Cc: netdev@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>