iptables: use dest_addr and dest_port for public port FORWARD rule

Docker-DCO-1.1-Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> (github: jpoimboe)
Merge pull request #3922 from jpoimboe/iptables-public-dest-port-fix

iptables: use dest_addr and dest_port for public port FORWARD rule