Neutron: MTU settings are now sane, so remove from DevStack

Neutron had a lot of work done during the Mitaka cycle to fix MTU
issues, so let's see if Neutron can stand on its own.

This commit reverts 06cfce37560243d22cd05b2c620be6702528a0b1

Neutron patches:
I6ffc8973c9b8f46cc19922ff04fdd2d23646b878
I4096a3e7704032fa4aa5c3aa8bcaec4e38d0d06d
I6a10c4dfc1f2198667f3d02528e2ca8020cb5bb8
Ic091fa78dfd133179c71cbc847bf955a06cb248a
Idf6221fee2c7da86123b330ad3c235ecc6868242
I6859ebdde1f7e3a8163b49d705620e522ada606a

Change-Id: Ie88c7ebb29adadde530217c95e2f38aacb119dc8
diff --git a/doc/source/guides/neutron.rst b/doc/source/guides/neutron.rst
index cac7bb0..1c43c11 100644
--- a/doc/source/guides/neutron.rst
+++ b/doc/source/guides/neutron.rst
@@ -443,13 +443,18 @@
 Non-Standard MTU on the Physical Network
 ----------------------------------------
 
-DevStack defaults to assume that the MTU on the physical network
-is 1500.  A different MTU can be specified by adding the following to
-the `localrc` part of `local.conf` on each machine.
+Neutron by default uses a MTU of 1500 bytes, which is
+the standard MTU for Ethernet.
+
+A different MTU can be specified by adding the following to
+the Neutron section of `local.conf`. For example,
+if you have network equipment that supports jumbo frames, you could
+set the MTU to 9000 bytes by adding the following
 
 ::
 
-    Q_ML2_PLUGIN_PATH_MTU=1500
+    [[post-config|/$Q_PLUGIN_CONF_FILE]]
+    global_physnet_mtu = 9000
 
 
 Disabling Next Generation Firewall Tools
diff --git a/lib/neutron_plugins/ml2 b/lib/neutron_plugins/ml2
index 0483ef1..30e1b03 100644
--- a/lib/neutron_plugins/ml2
+++ b/lib/neutron_plugins/ml2
@@ -40,12 +40,6 @@
 # L3 Plugin to load for ML2
 ML2_L3_PLUGIN=${ML2_L3_PLUGIN:-neutron.services.l3_router.l3_router_plugin.L3RouterPlugin}
 
-# Underlying path MTU for physical network managing br-tun; use '-' instead of
-# ':-' to allow people to explicitly override this to blank, to disable
-# automatic MTU calculation for tunnelled tenant networks
-Q_ML2_PLUGIN_PATH_MTU=${Q_ML2_PLUGIN_PATH_MTU-1500}
-
-
 function populate_ml2_config {
     CONF=$1
     SECTION=$2
@@ -83,12 +77,6 @@
         echo "WARNING - The ml2 plugin is using local tenant networks, with no connectivity between hosts."
     fi
 
-    # Enable ml2 mtu calculation mechanism for networks by providing path mtu
-    # value for physical devices that are used for br-tun traffic
-    if [[ "$ENABLE_TENANT_TUNNELS" == "True" ]] && [[ "$Q_ML2_PLUGIN_PATH_MTU" != "" ]]; then
-        iniset /$Q_PLUGIN_CONF_FILE ml2 path_mtu "$Q_ML2_PLUGIN_PATH_MTU"
-    fi
-
     # Allow for overrding VLAN configuration (for example, to configure provider
     # VLANs) by first checking if Q_ML2_PLUGIN_VLAN_TYPE_OPTIONS is set.
     if [ "$Q_ML2_PLUGIN_VLAN_TYPE_OPTIONS" == "" ]; then