Revert "geneve: pull IP header before ECN decapsulation"

This reverts commit 4179b00c04 ("geneve: pull IP header before ECN decapsulation").

Eric says: "network header should have been pulled already before
hitting geneve_rx()". Let's revert the syzbot fix since it's causing
more harm than good, and revisit.

Suggested-by: Eric Dumazet <edumazet@google.com>
Reported-by: Jianlin Shi <jishi@redhat.com>
Fixes: 4179b00c04 ("geneve: pull IP header before ECN decapsulation")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=210569
Link: https://lore.kernel.org/netdev/CANn89iJVWfb=2i7oU1=D55rOyQnBbbikf+Mc6XHMkY7YX-yGEw@mail.gmail.com/
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/geneve.c

@@ -257,21 +257,11 @@ static void geneve_rx(struct geneve_dev *geneve, struct geneve_sock *gs,
 		skb_dst_set(skb, &tun_dst->dst);
 
 	/* Ignore packet loops (and multicast echo) */
-	if (ether_addr_equal(eth_hdr(skb)->h_source, geneve->dev->dev_addr))
-		goto rx_error;
-
-	switch (skb_protocol(skb, true)) {
-	case htons(ETH_P_IP):
-		if (pskb_may_pull(skb, sizeof(struct iphdr)))
-			goto rx_error;
-		break;
-	case htons(ETH_P_IPV6):
-		if (pskb_may_pull(skb, sizeof(struct ipv6hdr)))
-			goto rx_error;
-		break;
-	default:
-		goto rx_error;
+	if (ether_addr_equal(eth_hdr(skb)->h_source, geneve->dev->dev_addr)) {
+		geneve->dev->stats.rx_errors++;
+		goto drop;
 	}
+
 	oiph = skb_network_header(skb);
 	skb_reset_network_header(skb);
 
@@ -308,8 +298,6 @@ static void geneve_rx(struct geneve_dev *geneve, struct geneve_sock *gs,
 		dev_sw_netstats_rx_add(geneve->dev, len);
 
 	return;
-rx_error:
-	geneve->dev->stats.rx_errors++;
 drop:
 	/* Consume bad packet */
 	kfree_skb(skb);