BUG/MINOR: args: add name for ARGT_VAR

Commit 4834bc7 ("MEDIUM: vars: adds support of variables") introduced
ARGT_VAR but forgot to put it in the names array. No backport needed.

include/types/arg.h

@@ -60,6 +60,7 @@ enum {
 	ARGT_MAP,      /* a pointer to a map descriptor */
 	ARGT_REG,      /* a pointer to a regex */
 	ARGT_VAR,      /* contains a variable description. */
+	/* please update arg_type_names[] in args.c if you add entries here */
 };
 
 /* context where arguments are used, in order to help error reporting */

src/arg.c

@@ -34,6 +34,7 @@ const char *arg_type_names[ARGT_NBTYPES] = {
 	[ARGT_USR]  = "user list",
 	[ARGT_MAP]  = "map",
 	[ARGT_REG]  = "regex",
+	[ARGT_VAR]  = "variable",
 	/* Unassigned types must never happen. Better crash during parsing if they do. */
 };