Lock the vnode interlock while reading v_usecount to update si_usecount in a cdev in devfs_reclaim().
Lock the vnode interlock while reading v_usecount to update si_usecount
in a cdev in devfs_reclaim().

MFC after:	3 days
Reviewed by:	jeff (a while ago)

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