fsal-proxy: Fix a NFS4ERR_BAD_SEQID bug in pxy_open_confirm()

As specified in RFC 3530 14.2.18, "the seqid passed to the OPEN_CONFIRM must be
1 greater than the seqid passed to the OPEN operation from which the
open_confirm value was obtained."  In pxy_create(), the seqid passed to OPEN
args is 0; the opok->stateid->seqid returned by OPEN is 1.  Therefore, the seqid
passed to OPEN_CONFIRM should be 1, which is exactly stateid->seqid.  The
unnecessary " + 1" makes seqid = 2 and causes a NFS4ERR_BAD_SEQID error.

Signed-off-by: Ming Chen <mchen@cs.stonybrook.edu>