IB/mthca: Make fw_cmd_doorbell default to 0

Setting fw_cmd_doorbell allows FW command to be queued using posted
writes instead of requiring polling on a "go" bit, so it should be a
performance boost.  However, the option causes problems with at least
some device/firmware combinations, so set the default to 0 until we
understand what's going on better.
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/hw/mthca/mthca_cmd.c

@@ -182,7 +182,7 @@ struct mthca_cmd_context {
 	u8                status;
 };
 
-static int fw_cmd_doorbell = 1;
+static int fw_cmd_doorbell = 0;
 module_param(fw_cmd_doorbell, int, 0644);
 MODULE_PARM_DESC(fw_cmd_doorbell, "post FW commands through doorbell page if nonzero "
 		 "(and supported by FW)");