net: fix vlan validation

VLAN identifiers are 12-bit decimal numbers, not IP addresses.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Reviewed-by: Tom Rini <trini@konsulko.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/include/env_flags.h b/include/env_flags.h
index 9e87e1b..0dcec06 100644
--- a/include/env_flags.h
+++ b/include/env_flags.h
@@ -57,8 +57,8 @@
 	"gatewayip:i," \
 	"netmask:i," \
 	"serverip:i," \
-	"nvlan:i," \
-	"vlan:i," \
+	"nvlan:d," \
+	"vlan:d," \
 	"dnsip:i,"
 #else
 #define ETHADDR_FLAGS