Broken link in the 'Controlling the Default Multicast Address with -u' section

Fix the upstream source that produced the broken HTML that Michael Bornholdt Nielsen fixed at https://github.com/wildfly/wildfly.github.io/pull/49/files#diff-5f2f4db1bf7cdf589ede5f35aad3953f3fbfe268040d7595f140dc4684976fe0

That PR made HTML fixes in additional places in some of the older doc versions, but for those the adoc no longer has the problem.