net: dccp: 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. Adds a pointer back to the sock.

Cc: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Soheil Hassas Yeganeh <soheil@google.com>
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
Cc: Eric Dumazet <edumazet@google.com>
Cc: dccp@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>