changelog: fix Closes statement

Lintian request the ':', so fix the statement.

Signed-off-by: Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>
rules: fix clean op

By default, dh_auto_clean tries `make -j1 distclean'.
However, the makefile by Netfilter doesn't implement that operation.

So override with a simpler `make clean'.

Signed-off-by: Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>