netfilter: xt_osf: change %pi4 to %pI4

commit 8a27f7c9
changed the output style of %pi4 to use fixed
width leading zero IP addresses "001.002.003.004".

It's useful when printing multiple lines of
addresses, but was a change in output style for
some existing uses.

Using %pI4 restores the previous output style.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>