net/decnet: Convert timers to use timer_setup()

net/decnet: Convert timers to use timer_setup()

In preparation for unconditionally passing the struct timer_list pointer to
all timer callbacks, switch to using the new timer_setup() and from_timer()
to pass the timer pointer explicitly.

Cc: "David S. Miller" <[email protected]>
Cc: Johannes Berg <[email protected]>
Cc: David Ahern <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Kees Cook <[email protected]>
Signed-off-by: David S. Miller <[email protected]>