kernel-resin.bbclass: Add config for supporting iptables packet filtering REJECT target
kernel-resin.bbclass: Add config for supporting
iptables packet filtering REJECT target

The iptables REJECT target is needed by the resin.io supervisor to
create the iptables rules for the API

Signed-off-by: Florin Sarbu <3a837a37a2ac9072a088641ec330e0e5d5b86f4e@resin.io>

resin-os/meta-resin,resin-os/meta-resin,resin-os/meta-resin,resin-os/meta-resin