OFAgent: Avoid re-wiring ports unnecessarily

Port the following patch to OFAgent.
commit: a9050757d94009c68f06c9f374de33eefbf06aa9
https://review.openstack.org/#/c/63558/

Partial-Bug: 1293265

Change-Id: I35d58bad104b01136c2502c933475ac85a3752a5
(cherry picked from commit fcdee4d44558b6d1ae647f38b2584820352115de)
OFAgent: Improve handling of security group updates

Port the following patch to OFAgent.
commit: 3046c4ae22b10f9e4fa83a47bfe089554d4a4681
https://review.openstack.org/#/c/63100/

Partial-Bug: 1293265

Change-Id: Iecdfee894ff2fd5f05f63f040dd70821af124737
(cherry picked from commit 6e46769594c856647b0f9ab0dddbe6dd9c9163a1)
OFAgent: Fixing lost vlan ids on interfaces

Port the following patch to OFAgent.
commit: 60cb0911712ad11688b4d09e5c01ac39c49f5aea
https://review.openstack.org/#/c/66375/

Closes-Bug: #1309286

Change-Id: I04f99ef7928cd07959b29eb64b5744df397979b8
(cherry picked from commit c1827a074654d2e8d07e93945fa605ad3b6c18fb)
Merge "OFAgent: Avoid re-wiring ports unnecessarily" into stable/icehouse
Merge "OFAgent: Fixing lost vlan ids on interfaces" into stable/icehouse
Merge "OFAgent: Improve handling of security group updates" into stable/icehouse