userspace/tools: allow setting parameters for vid 0 in wrs_vlans

It was not possible to pass parameters when vid 0 was the first one specified
wrs1#wrs_vlans --rvid 0 --rdrop 1 --rvid 1 --rdrop 1
wrs_vlans: missing "--rvid <vid>" before rtu cmd
However, it was possible if any other vid was specified before:
wrs1#wrs_vlans --rvid 1 --rdrop 1 --rvid 0 --rdrop 1

Signed-off-by: Adam Wujek <adam.wujek@cern.ch>

userspace/tools/wrs_vlans.c

@@ -727,13 +727,13 @@ static int set_rtu_vlan(int vid, int fid, int pmask, int drop, int prio,
 {
 	struct rtu_vlans_t *cur = rtu_vlans;;
 
-	if (!rtu_vlans && vid <= 0) {
+	if (!rtu_vlans && vid < 0) {
 		fprintf(stderr, "%s: missing \"--rvid <vid>\" before rtu cmd\n",
 			prgname);
 		return -1;
 	}
 
-	if (vid > 0) {
+	if (vid >= 0) {
 		cur = calloc(1, sizeof(*cur));
 		if (!cur) {
 			fprintf(stderr, "%s: %s\n", prgname, strerror(errno));