package/iptables: bump version to 1.8.4

For changelog details see [1].

[1] https://netfilter.org/projects/iptables/files/changes-iptables-1.8.4.txt



Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>