Do not defer IPTables apply in firewall path

By default, iptables apply is deferred in L3 agent. For
external gateways, iptables is applied immediately (to
enable NAT for floating IP). Similarly, when firewall
is created/updated/deleted, iptable rules are applies
immediately.

Change-Id: I4f652a030ae23a71a2e20af2e8ef0ad5b882b80e
Closes-Bug: #1320775
Merge "Do not defer IPTables apply in firewall path"