The pnfsdskill(8) command will normally fail if there is no valid mirror
for the DS to be disabled. However, a system administrator may need to
disable a DS which does not have a valid mirror so that the nfsd threads
can be terminated. This patch adds the kernel code needed by pnfsdskill(8)
to implement this "forced" case of disabling a DS.
This patch only affects the pNFS server.