staging/lustre/mgc: replace hard-coded MGC_ENQUEUE_LIMIT value

During client mount, the client will send an LDLM_ENQUEUE request to
MGS with send delay set to MGC_ENQUEUE_LIMIT, which is hard coded to
50 seconds. On the other hand, the interval for pinger is deduced from
obd_timeout. When obd_timeout is configured for a longer period of
time, so does the pinger. We know that connecting to the secondary MGS
node is triggered by the pinger. Now that we have a longer interval,
the pinger will not be able to try the secondary before the
LDLM_ENQUEUE request fails the mount using the same delay limit.

This code change will replace the hard-coded send delay being
mentioned above with a value that is long enough to give the client a
chance to connect to the secondary MGS if exists.

Signed-off-by: Cheng Shao <cheng_shao@xyratex.com>
Reviewed-on: http://review.whamcloud.com/9217
Xyratex-bug-id: MRP-1516
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-4582
Reviewed-by: Ryan Haasken <haasken@cray.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/mgc/mgc_request.c

@@ -950,7 +950,10 @@ static int mgc_blocking_ast(struct ldlm_lock *lock, struct ldlm_lock_desc *desc,
 }
 
 /* Not sure where this should go... */
-#define  MGC_ENQUEUE_LIMIT 50
+/* This is the timeout value for MGS_CONNECT request plus a ping interval, such
+ * that we can have a chance to try the secondary MGS if any. */
+#define  MGC_ENQUEUE_LIMIT (INITIAL_CONNECT_TIMEOUT + (AT_OFF ? 0 : at_min) \
+				+ PING_INTERVAL)
 #define  MGC_TARGET_REG_LIMIT 10
 #define  MGC_SEND_PARAM_LIMIT 10