Update load-balancer-ipv6-overview.md

It's currently not possible to attach **secondary** NICs which refer to a IPv6 subnet to a Load Balancer's backend pool.

Author: heoelri

articles/load-balancer/load-balancer-ipv6-overview.md

@@ -76,6 +76,7 @@ Limitations
 * Changing the loadDistributionMethod parameter for IPv6 is **currently not supported**.
 * Reserved IPv6 IPs (where IPAllocationMethod = static) are **currently not supported**.
 * NAT64 (translation of IPv6 to IPv4) is not supported.
+* It's currently not supported to attach secondary NICs, that are refering to a IPv6 subnet, to a Backend Pool.
 
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