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
(cherry picked from commit 6167cb55e2f62a645487d66e52b809c9599b3bb8)
Merge "Do not defer IPTables apply in firewall path" into stable/icehouse