Needrestart might want to restart openvswitch-switch \\
Tried it once and all Xen domU's got disconnected.

<code diff>
--- /etc/needrestart/needrestart.conf~  2015-03-24 10:26:33.000000000 +0100
+++ /etc/needrestart/needrestart.conf   2015-12-04 16:56:14.000000000 +0100
@@ -68,6 +68,7 @@
     q(^openvpn) => 0,
     q(^quagga) => 0,
     q(^tinc) => 0,
+    q(^openvswitch-switch) => 0,
 
     # gettys
     q(^getty@.+\.service) => 0,
</code>

And also remove xendomains from the list (maybe xen should be added as well)

<code diff>
bigbang:~# diff -u /etc/needrestart/needrestart.conf~  /etc/needrestart/needrestart.conf
--- /etc/needrestart/needrestart.conf~  2015-12-04 16:56:14.000000000 +0100
+++ /etc/needrestart/needrestart.conf   2015-12-10 20:24:11.000000000 +0100
@@ -76,6 +76,7 @@
     # misc
     q(^zfs-fuse) => 0,
     q(^mythtv-backend) => 0,
+    q(^xendomains) => 0,
 
     # workaround for broken systemd-journald
     # (see also Debian Bug#771122 & #771254)
</code>