tools/xenstored: Wire properly the command line option -M/--path-max

The command line option -M/--path-max was meant to be added by
commit 924bf8c793 "tools/xenstore: rework path length check" but this
wasn't wired through properly.

Fix it by adding the missing "case 'M':".

Fixes: 924bf8c793 ("tools/xenstore: rework path length check")
Signed-off-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Luca Fancellu <luca.fancellu@arm.com>
Reviewed-by: Juergen Gross <jgross@suse.com>

tools/xenstore/xenstored_core.c

@@ -2148,6 +2148,7 @@ int main(int argc, char *argv[])
 		case 'A':
 			quota_nb_perms_per_node = strtol(optarg, NULL, 10);
 			break;
+		case 'M':
 			quota_max_path_len = strtol(optarg, NULL, 10);
 			quota_max_path_len = min(XENSTORE_REL_PATH_MAX,
 						 quota_max_path_len);