[DCCP]: Implement the CLOSING timer

So that we retransmit CLOSE/CLOSEREQ packets till they elicit an
answer or we hit a timeout.

Most of the machinery uses TCP approaches, this code has to be
polished & audited, but this is better than we had before.

Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc net/dccp/dccp.h
Simple merge

diff --cc net/dccp/input.c
Simple merge

diff --cc net/dccp/output.c
Simple merge

diff --cc net/dccp/proto.c
Simple merge