ip_tunnel_core: Change __skb_push back to skb_push

Git commit 0e6fbc5b ("ip_tunnels: extend iptunnel_xmit()")
moved the IP header installation to iptunnel_xmit() and
changed skb_push() to __skb_push(). This makes possible
bugs hard to track down, so change it back to skb_push().

Cc: Pravin Shelar <pshelar@nicira.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/ip_tunnel_core.c

@@ -61,7 +61,7 @@ int iptunnel_xmit(struct rtable *rt, struct sk_buff *skb,
 	memset(IPCB(skb), 0, sizeof(*IPCB(skb)));
 
 	/* Push down and install the IP header. */
-	__skb_push(skb, sizeof(struct iphdr));
+	skb_push(skb, sizeof(struct iphdr));
 	skb_reset_network_header(skb);
 
 	iph = ip_hdr(skb);