NSM: Add nsm_lookup() function

Introduce a new API to fs/lockd/mon.c that allows nlm_host_rebooted()
to lookup up nsm_handles via the contents of an nlm_reboot struct.

The new function is equivalent to calling nsm_find() with @create set
to zero, but it takes a struct nlm_reboot instead of separate
arguments.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
diff --git a/include/linux/lockd/lockd.h b/include/linux/lockd/lockd.h
index 2a3533e..5e3ad92 100644
--- a/include/linux/lockd/lockd.h
+++ b/include/linux/lockd/lockd.h
@@ -251,6 +251,7 @@
 					const char *hostname,
 					const size_t hostname_len,
 					const int create);
+struct nsm_handle *nsm_reboot_lookup(const struct nlm_reboot *info);
 void		  nsm_release(struct nsm_handle *nsm);
 
 /*