Ensure that FORWARD rule also supports DHCP

The previous fix only addressed the INPUT rules and not the
FORWARD rule.

Adds FORWARD rule to ensure that DHCP traffic is forwarded correctly.

Fixes bug 1131223

Change-Id: Ie0d365ba1ba1014bdd2bfc944123c17c4e415d6e
Merge "Ensure that FORWARD rule also supports DHCP"