Break retry loop on success in dhcp-all-interfaces

If rdisc6 is available, a node using this element will loops until
DIB_DHCP_TIMEOUT is reached because of a missing 'break' when rdisc6
return code is 0.
This will mark the dhcp-interface@.service unit as failed (because it
has the same timeout) and not bring any network interface online.

Change-Id: I034dcda94d765f236950ebcbee36789f5bdc515f
Closes-Bug: #1854717
Signed-off-by: Hervé Rousseau <hroussea@cern.ch>

diskimage_builder/elements/dhcp-all-interfaces/install.d/dhcp-all-interfaces.sh

@@ -162,6 +162,7 @@ function inspect_interface() {
                         ipv6_init=True
                         ipv6_AdvManagedFlag=$(echo "$RA" | grep "Stateful address conf." | awk -F: '{ print $2 }')
                         ipv6_AdvOtherConfigFlag=$(echo "$RA" | grep "Stateful other conf." | awk -F: '{ print $2 }')
+                        break
                     elif [ $return_code -eq 1 ]; then
                         sleep 1
                     elif [ $return_code -eq 2 ]; then

releasenotes/notes/fix_rdisc6_loop-32a308a97de99f0f.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    The ``dhcp-all-interfaces`` element could not configure network interfaces
+    properly when ``rdisc6`` is present on the system