net-firewall/nftables: Minor fixes on the script closes #675188

net-firewall/nftables: Minor fixes on the script closes #675188

* Use printf instead of echo for better shell compatibility.
* Use an include instead of concatenating the ruleset.
  (Note that this is likely to fail is the ruleset path contains
   special characters).
* Empty the table first when executing panic actions.

Fixes: https://bugs.gentoo.org/675188

Signed-off-by: Francisco Blas Izquierdo Riera (klondike) <klondike@gentoo.org>
Package-Manager: Portage-2.3.51, Repoman-2.3.11
Signed-off-by: Matthew Thode <prometheanfire@gentoo.org>