Remove RPC to plugin when dhcp sets default route

_set_default_route() was using an RPC to the plugin to get the DHCP
port for the network on the current host, and then used it to form
the tap device name. This happened on every allocation reload too.
This fix removes the RPC and gets the tap device name using local
methods instead. It also removes an unnecessary call to set the
default route in the restart method.

Closes-Bug: 1290068
Related-Bug: 1294254
Change-Id: I639bcf93725c4969d1011d2d20491d461ccfdbed
Ml2: Set correct nullable for admin_state_up

In migrations 492a106273f8_brocade_ml2_mech_dri was set incorrect
nullable parameter:

Set admin_state_up NOT NULL in ml2_brocadeports.

Partial-Bug: #1296282

Change-Id: I051e37990ae3371978eeb1ff71e70ae2a44097bc
Cisco: Set correct nullable for switch_ip, instance_id, vlan_id

Corrected the following model according to database
content:
 - NOT NULL for NexusPortBinding switch_ip and instance_id

In migrations folsom_initial was set incorrect nullable parameter:
- Set vlan_id NOT NULL in cisco_nexusport_bindings.

Partial-Bug: #1296282

Change-Id: Ie5315fcbf227025c30ab4a4b97ec2a140ee3923c
ip-lib : use "ip neigh replace" instead of "ip neigh add"

Closes bug #1311002

Change-Id: Ie50bc0bff32b7f97ac317ccc2521bbea52d59ca3
Merge "Ml2: Set correct nullable for admin_state_up"
Merge "Remove RPC to plugin when dhcp sets default route"
Merge "ip-lib : use "ip neigh replace" instead of "ip neigh add""
Merge "Cisco: Set correct nullable for switch_ip, instance_id, vlan_id"