Restart ivs/nvfswitch after config file is updated

This change - https://review.openstack.org/#/c/561609/, removed the
restart of ivs/nvfswitch to avoid network interruptions. However,
when a change is made to the config file then ivs/nvfswitch must be
restarted in order to pick up the change.

Closes-Bug: #1794182
Change-Id: I8f879072799cef29c09ddc74bd71069dd168ec88
(cherry picked from commit 2495c9ddaa)

os_net_config/impl_ifcfg.py

@@ -1110,13 +1110,21 @@ class IfcfgNetConfig(os_net_config.NetConfig):
         if ivs_uplinks or ivs_interfaces:
             location = ivs_config_path()
             data = self.generate_ivs_config(ivs_uplinks, ivs_interfaces)
-            self.write_config(location, data)
+            if (utils.diff(location, data)):
+                self.write_config(location, data)
+                msg = "Restart ivs"
+                self.execute(msg, '/usr/bin/systemctl',
+                             'restart', 'ivs')
 
         if nfvswitch_interfaces or nfvswitch_internal_ifaces:
             location = nfvswitch_config_path()
             data = self.generate_nfvswitch_config(nfvswitch_interfaces,
                                                   nfvswitch_internal_ifaces)
-            self.write_config(location, data)
+            if (utils.diff(location, data)):
+                self.write_config(location, data)
+                msg = "Restart nfvswitch"
+                self.execute(msg, '/usr/bin/systemctl',
+                             'restart', 'nfvswitch')
 
         if activate:
             for linux_team in restart_linux_teams:

releasenotes/notes/restart-ivs-nvfswitch-after-change-0825ea78aae8f138.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - When the ivs interface (or nfvswitch) configuration changes,
+    ivs (or nvfswitch) needs to be restarted in order to pick
+    up the new configuration.