Server must enforce utf8 encoding for the compound 'tag' argument.
Compound request with an invalid 'tag' should be replied with NFS4ERR_INVAL
Fix problems in DESTROY_SESSSION and DESTROY_CLIENTID
DESTROY_SESSION can only be invoked on a connection associated with the session
DESTROY_CLIENTID on a non-existent CLIENTID should return STALE_CLIENTID