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
Merge "Fix IP spoofing filter blocking all packets."