Allow implicit "convert" to the same lock mode.

(Code already not fail if unlocking not locked resource.)

This is needed in pre/post lock_lv call, where we can
request the same lock on local node becuase of suspend call.

WHATS_NEW

@@ -1,5 +1,6 @@
 Version 2.02.57 -
 ====================================
+  Allow implicit convert to the same cluster lock mode.
   Replace magic masks in cluster locking code by defined masks.
   Remove log volume from metadata if initial deactivation fails.
   Give better error message for pvmove when all data is skipped.

daemons/clvmd/lvm-functions.c

@@ -245,6 +245,11 @@ int hold_lock(char *resource, int mode, int flags)
 
 	lvi = lookup_info(resource);
 
+	if (lvi && lvi->lock_mode == mode) {
+		DEBUGLOG("hold_lock, lock mode %d already held\n", mode);
+		return 0;
+	}
+
 	/* Only allow explicit conversions */
 	if (lvi && !(flags & LKF_CONVERT)) {
 		errno = EBUSY;