nfs41: consider minorversion in callback_xdr:process_op

Note that this patch changes the nfsv4.0 behavior also when
CONFIG_NFS_V4_1 is not defined where NFS4ERR_MINOR_VERS_MISMATCH
will be returned if the client received a CB_COMPOUND
with minorversion != 0.  Previously, it would have
returned NFS4ERR_OP_ILLEGAL for CB_SEQUENCE.
(or if the server is broken and sent OP_CB_GETATTR or OP_CB_RECALL
with minorversion!=0, they would have been processed normally.

Signed-off-by: Benny Halevy <bhalevy@panasas.com>
[nfs41: refactor op preprocessing out of process_op]
See http://linux-nfs.org/pipermail/pnfs/2009-June/007845.html
[nfs41: define CB_NOTIFY_DEVICEID as not supported]
Signed-off-by: Benny Halevy <bhalevy@panasas.com>