ea: assign superblock to named attribute directory

the upcall to set an EA was crashing in nfs41_open() on a null superblock, because nfs41_rpc_openattr() was returning a filehandle without a superblock.  copy the parent file's superblock to the returned filehandle

Signed-off-by: Casey Bodley <cbodley@citi.umich.edu>

daemon/nfs41_ops.c

@@ -2186,6 +2186,8 @@ enum nfsstat4 nfs41_rpc_openattr(
         goto out;
 
     compound_error(status = compound.res.status);
+
+    fh_out->superblock = file->fh.superblock;
 out:
     return status;
 }