Fix SIGSEGV while preforming INSTCMD

https://github.com/networkupstools/nut/pull/2155

--- nut-2.8.1.x/drivers/dstate.c	2023-09-19 10:08:14.000000000 +0200
+++ nut-2.8.1/drivers/dstate.c	2023-11-09 04:46:33.193533124 +0100
@@ -780,7 +780,7 @@
 			upsdebugx(3, "%s: TRACKING = %s", __func__, cmdid);
 
 		/* try the handler shared by all drivers first */
-		ret = main_instcmd(arg[1], arg[2], conn);
+		ret = main_instcmd(cmdname, cmdparam, conn);
 		if (ret != STAT_INSTCMD_UNKNOWN) {
 			/* The command was acknowledged by shared handler, and
 			 * either handled successfully, or failed, or was not