Use CTLFLAG_RDTUN for read-only sysctl that exports tunable.
Use CTLFLAG_RDTUN for read-only sysctl that exports tunable.

Reminded by:	pjd
MFC after:	6 days

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