Add a comment for the ccv member of struct tcpcb.
Add a comment for the ccv member of struct tcpcb.

Sponsored by:	FreeBSD Foundation
MFC after:	5 weeks
X-MFC with:	r215166

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