nfsd4: allow setting grace period time

Allow explicit configuration of the grace period time as well as the
lease period time.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

fs/nfsd/nfsd.h

@@ -228,6 +228,7 @@ extern struct timeval	nfssvc_boot;
 #ifdef CONFIG_NFSD_V4
 
 extern time_t nfsd4_lease;
+extern time_t nfsd4_grace;
 
 /* before processing a COMPOUND operation, we have to check that there
  * is enough space in the buffer for XDR encode to succeed.  otherwise,