Fix IP spoofing filter blocking all packets.

Implement IP spoofing filter by adding yet another chain to iptables
with RETURN rule for each of IP addresses assigned to port and DROP
rule at the end of the chain.

Fixes: bug #1190613
Change-Id: I2e7a0f8dd4c3519c57d28e87a44735a3482624b1
(cherry picked from commit 531ff2fb34df9e6b0f84ada811c29240f0f1cd48)
Merge "Fix IP spoofing filter blocking all packets." into stable/grizzly