netfilter: Remove leading spaces in Kconfig

Remove leading spaces before tabs in Kconfig file(s) by running the
following command:

  $ find net/netfilter -name 'Kconfig*' | xargs sed -r -i 's/^[ ]+\t/\t/'
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>