Insist that the first time a client presents a new lockowner, the seqid should
be 0.  (RFC 3530 section 8.1.5)

Also, return an error if the client presents a previously-used lockowner as if
it were new.

From: Andy Adamson <andros@citi.umich.edu>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>        
Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>