neutron: Use update-alternatives --display instead of --query

--query is not supported before update-alternatives 1.15
and CentOS uses 1.13

Closes-Bug: #1936947
Change-Id: I78da7eb2b6b5eae2b04fd95b24615bd4a572a1d6

docker/neutron/neutron-base/extend_start.sh

@@ -13,7 +13,8 @@ else
 fi
 
 # set legacy iptables to allow kernels not supporting iptables-nft
-if $UPDATE_ALTERNATIVES --query iptables; then
+# CentOS has update-alternatives 1.13, so use --display (not --query)
+if $UPDATE_ALTERNATIVES --display iptables; then
     # NOTE(yoctozepto): Kolla-Ansible does not always set KOLLA_LEGACY_IPTABLES;
     # the workaround below ensures it gets set to `false` in such cases to fix
     # this code under `set -o nounset`.

releasenotes/notes/bug-1936947-8beac926823cdf8f.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    Fixes wrong update-alternatives usage on CentOS.
+    `LP#1936947 <https://launchpad.net/bugs/1936947>`__