iptables: do not print trailing whitespaces

iptables: do not print trailing whitespaces

Due to the use of printf("foobar "), iptables emits spaces at the
end-of-line, which looks odd to some users because it causes the
terminal to wrap even if there is seemingly nothing to print.

It may also have other points of annoyance, such as mailers
interpreting a trailing space as an indicator that the paragraph
continues when format=flowed is also on.
And git highlights trailing spaces in red, so let's avoid :)

Preexisting inconsistencies in outputting spaces in the right
spot are also addressed right away.

References: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=429579
Signed-off-by: Jan Engelhardt <jengelh@medozas.de>