Add note on restricted support

source/adminguide/networking/multi_vlan_trunk_nics.rst

diff --git a/source/adminguide/networking/multi_vlan_trunk_nics.rst b/source/adminguide/networking/multi_vlan_trunk_nics.rst
index 0fa32b0..32aa0cb 100644
--- a/source/adminguide/networking/multi_vlan_trunk_nics.rst
+++ b/source/adminguide/networking/multi_vlan_trunk_nics.rst
@@ -208,6 +208,12 @@
    with ``vlan.filtering.enabled``, see Migration Behavior below for the
    full picture across host capability combinations.
 
+-  Multi-VLAN trunk NICs are supported only in zones with a single Guest
+   physical network. A host's VLAN filtering readiness is detected per
+   host, not per physical network, so it is only guaranteed correct when
+   there is exactly one. Using trunk NICs in a zone with more than one
+   Guest physical network is unsupported in this release.
+
 Associating and Disassociating Networks
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~