BUG 11318: Fix deletion of temporary files from IPTables-GUI

BUG 11318: Fix deletion of temporary files from IPTables-GUI

For details see:
https://bugzilla.ipfire.org/show_bug.cgi?id=11318

Temporary files for 'iptables', 'iptablesmangle' and 'iptablesnat' created by
'iptables.cgi' were not deleted after use but stayed in '/srv/weg/ipfire/html/'.

As a workaround I changed 'getipstat.c' to create these files in '/var/tmp' and the
"open (file..." and "rm" commands in 'iptables.cgi'.

Works here.

Best,
Matthias

Signed-off-by: Matthias Fischer <matthias.fischer@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>