ip_gre: Add IPPROTO_GRE to flowi in ipgre_tunnel_xmit

Commit 5811662b15 ("net: use the macros
defined for the members of flowi") accidentally removed the setting of
IPPROTO_GRE from the struct flowi in ipgre_tunnel_xmit. This patch
restores it.

Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Acked-by: Changli Gao <xiaosuo@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/ip_gre.c

@@ -775,6 +775,7 @@ static netdev_tx_t ipgre_tunnel_xmit(struct sk_buff *skb, struct net_device *dev
 			.fl4_dst = dst,
 			.fl4_src = tiph->saddr,
 			.fl4_tos = RT_TOS(tos),
+			.proto = IPPROTO_GRE,
 			.fl_gre_key = tunnel->parms.o_key
 		};
 		if (ip_route_output_key(dev_net(dev), &rt, &fl)) {