NFSD: fix seqid in copy stateid

NFSD: fix seqid in copy stateid

s_stid->si_generation is a u32, copy->stateid.seqid is a __be32, so we
should be byte-swapping here if necessary.

This effectively undoes the byte-swap performed when reading
s_stid->s_generation in nfsd4_decode_copy().  Without this second swap,
the stateid we sent to the source in READ could be different from the
one the client provided us in the COPY.  We didn't spot this in testing
since our implementation always uses a 0 in the seqid field.  But other
implementations might not do that.

You'd think we should just skip the byte-swapping entirely, but the
s_stid field can be used for either our own stateids (in the
intra-server case) or foreign stateids (in the inter-server case), and
the former are interpreted by us and need byte-swapping.

Reported-by: kbuild test robot <lkp@intel.com>
Fixes: d5e54eeb0e3d ("NFSD add nfs4 inter ssc to nfsd4_copy")
Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>