erspan: get the proto with the md version for collect_md

In commit 20704bd1 ("erspan: build the header with the right proto
according to erspan_ver"), it gets the proto with t->parms.erspan_ver,
but t->parms.erspan_ver is not used by collect_md branch, and instead
it should get the proto with md->version for collect_md.

Thanks to Kevin for pointing this out.

Fixes: 20704bd1 ("erspan: build the header with the right proto according to erspan_ver")
Fixes: 94d7d8f2 ("ip6_gre: add erspan v2 support")
Reported-by: NKevin Traynor <ktraynor@redhat.com>
Signed-off-by: NXin Long <lucien.xin@gmail.com>
Reviewed-by: NSimon Horman <simon.horman@corigine.com>
Reviewed-by: NWilliam Tu <u9012063@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/ip6_gre.c

@@ -1015,12 +1015,14 @@ static netdev_tx_t ip6erspan_tunnel_xmit(struct sk_buff *skb,
 					    ntohl(tun_id),
 					    ntohl(md->u.index), truncate,
 					    false);
+			proto = htons(ETH_P_ERSPAN);
 		} else if (md->version == 2) {
 			erspan_build_header_v2(skb,
 					       ntohl(tun_id),
 					       md->u.md2.dir,
 					       get_hwid(&md->u.md2),
 					       truncate, false);
+			proto = htons(ETH_P_ERSPAN2);
 		} else {
 			goto tx_err;
 		}
@@ -1043,24 +1045,25 @@ static netdev_tx_t ip6erspan_tunnel_xmit(struct sk_buff *skb,
 			break;
 		}
 
-		if (t->parms.erspan_ver == 1)
+		if (t->parms.erspan_ver == 1) {
 			erspan_build_header(skb, ntohl(t->parms.o_key),
 					    t->parms.index,
 					    truncate, false);
-		else if (t->parms.erspan_ver == 2)
+			proto = htons(ETH_P_ERSPAN);
+		} else if (t->parms.erspan_ver == 2) {
 			erspan_build_header_v2(skb, ntohl(t->parms.o_key),
 					       t->parms.dir,
 					       t->parms.hwid,
 					       truncate, false);
-		else
+			proto = htons(ETH_P_ERSPAN2);
+		} else {
 			goto tx_err;
+		}
 
 		fl6.daddr = t->parms.raddr;
 	}
 
 	/* Push GRE header. */
-	proto = (t->parms.erspan_ver == 1) ? htons(ETH_P_ERSPAN)
-					   : htons(ETH_P_ERSPAN2);
 	gre_build_header(skb, 8, TUNNEL_SEQ, proto, 0, htonl(atomic_fetch_inc(&t->o_seqno)));
 
 	/* TooBig packet may have updated dst->dev's mtu */