Fix the reference for the IPV6_V6ONLY option.  This option is described in RFC 3493, not 3542.
Fix the reference for the IPV6_V6ONLY option.  This option is described
in RFC 3493, not 3542.

PR:		docs/134127
Submitted by:	Kenji Rikitake <kenji.rikitake@acm.org>
MFC after:	2 weeks

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase