VLANs -- move work-around details to User Guide

Much of the RN info was already duplicated in the User Guide;
now the User Guide has all the information and the RN has just
a brief statement about the issue and a link to the User Guide.

No content changes in the information here, just one slight
rewrite.

Change-Id: I115a9e744ab7b44d885c7a1d3df2f9b538caae72