Change the pNFS server so that it does not disable a mirrored DS when a
client does a LayoutReturn with an error report of NFSERR_STALE from a DS.
The current FreeBSD client can generate these errors for an operational
DS while doing a recovery of a mirror after a mirrored DS has been repaired.
I am not sure why these errors occur, but my best current guess is a race between
the Layout Recall issued by the kernel code run from pnfsdscopymr(8) and a
Read operation on the DS for the file bing copied.
The errrors are not fatal, since the client falls back on doing I/O through
the MDS, which can do the I/O successfully as a proxy. (The fact that the
MDS can do this indicates that the file does still exist on the functioning
DS.)