[qca-nss-sfe] Support VLAN offload in SFE in Tun6rd

VLAN tagging(encapsulation) and untag(decapsulation)
can be accelerated in SFE for Tun6rd.

Signed-off-by: Tian Yang <quic_tiany@quicinc.com>
Change-Id: If79b930f8c4ff194e48f209bb63be639913093be
diff --git a/sfe_ipv4.h b/sfe_ipv4.h
index edec758..f19adb1 100644
--- a/sfe_ipv4.h
+++ b/sfe_ipv4.h
@@ -190,6 +190,8 @@
 	u16 pppoe_session_id;
 	u8 pppoe_remote_mac[ETH_ALEN];
 
+	struct net_device *top_interface_dev;	/* Used by tun6rd to store decap VLAN netdevice.*/
+
 	/*
 	 * Size of all needed L2 headers
 	 */