Skips enabling kernel bridge firewall in container

Calling enable_kernel_bridge_firewall inside a
container, devstack will crash because it tries to
load a kernel module by calling 'sudo modprobe' on
net.bridge.

Change-Id: Id4718c065d5a8c507d49f38e19c2796a64221aa4
Closes-Bug: #1662194
diff --git a/lib/neutron b/lib/neutron
index f6c705c..a43fdeb 100644
--- a/lib/neutron
+++ b/lib/neutron
@@ -188,7 +188,9 @@
             iniset $NEUTRON_CORE_PLUGIN_CONF ovs local_ip $HOST_IP
         fi
 
-        enable_kernel_bridge_firewall
+        if ! running_in_container; then
+            enable_kernel_bridge_firewall
+        fi
     fi
 
     # DHCP Agent