SUNRPC/NFSD: Change to type of bool for rq_usedeferral and rq_splice_ok

rq_usedeferral and rq_splice_ok are used as 0 and 1, just defined to bool.

Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>