NSX: fix router ports port_security_enabled=False

Previously there was a bug that resulted in a security group being
added to router ports which was not supported in NSX. Removing the
security group didn't actually completely solve the problem as we
never cleared the allowed_address_pairs on the router port. This
patch fixes this issue by disabling port_security_enabled on the
router port.

Change-Id: Ib61756e3bd5866318cbc3bb9856344571399d656
Closes-bug: 1344266
Related-bug: 1329043
(cherry picked from commit 25f1439ff356f78ab0d28a74dfc75d50e2f030b6)
Merge "NSX: fix router ports port_security_enabled=False" into stable/icehouse