net-firewall/iptables: allow for iptables' module autoload functionality

net-firewall/iptables: allow for iptables' module autoload functionality

In commit cdc003118830087bbb409761fe4e0e2c19ea103a, a non working check
were fixed. In addition, error handling was added.
However, this introduced a behavior change for users who didn't load
iptables on their own and relied on iptables' own capability to autoload
required modules.

This new revision restores previous behavior and allows for relying on
iptables' module autoload capability again.

Closes: https://bugs.gentoo.org/672366
Package-Manager: Portage-2.3.52, Repoman-2.3.12
Signed-off-by: Thomas Deutschmann <whissi@gentoo.org>