common: parsing_headers.h reduce default VLAN depth to 2

Given XDP is very performance focused, it is unwise to default
parse many VLAN layers.  Those 2 as it is very uncommon to have more.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>

Author: netoptimizer

common/parsing_helpers.h

@@ -56,7 +56,7 @@ struct icmphdr_common {
 
 /* Allow users of header file to redefine VLAN max depth */
 #ifndef VLAN_MAX_DEPTH
-#define VLAN_MAX_DEPTH 4
+#define VLAN_MAX_DEPTH 2
 #endif
 
 static __always_inline int proto_is_vlan(__u16 h_proto)