MFC: Close a race in the kern.ttys sysctl handler that resulted in panics in dev2udev().
MFC: Close a race in the kern.ttys sysctl handler that resulted in panics
in dev2udev().

Approved by:	re (gnn)

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