Revert "sit: reload iphdr in ipip6_rcv"

BugLink: http://bugs.launchpad.net/bugs/1772775

This reverts commit b699d003.

As per Eric Dumazet, the pskb_may_pull() is a NOP in this
particular case, so the 'iph' reload is unnecessary.
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit f4eb17e1)
Signed-off-by: Joseph Salisbury <joseph.salisbury@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>

net/ipv6/sit.c

@@ -692,7 +692,6 @@ static int ipip6_rcv(struct sk_buff *skb)
 
 		if (iptunnel_pull_header(skb, 0, htons(ETH_P_IPV6)))
 			goto out;
-		iph = ip_hdr(skb);
 
 		err = IP_ECN_decapsulate(iph, skb);
 		if (unlikely(err)) {