net/ip_tunnels: Introduce tunnel_id_to_key32() and key32_to_tunnel_id()

Add utility functions to convert a 32 bits key into a 64 bits tunnel and
vice versa.
These functions will be used instead of cloning code in GRE and VXLAN,
and in tc act_iptunnel which will be introduced in a following patch in
this patchset.

Signed-off-by: Amir Vadai <amir@vadai.me>
Signed-off-by: Hadar Hen Zion <hadarh@mellanox.com>
Reviewed-by: Shmulik Ladkani <shmulik.ladkani@gmail.com>
Acked-by: Jiri Benc <jbenc@redhat.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 113cc43..576f705 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -246,25 +246,6 @@
 	ipgre_err(skb, info, &tpi);
 }
 
-static __be64 key_to_tunnel_id(__be32 key)
-{
-#ifdef __BIG_ENDIAN
-	return (__force __be64)((__force u32)key);
-#else
-	return (__force __be64)((__force u64)key << 32);
-#endif
-}
-
-/* Returns the least-significant 32 bits of a __be64. */
-static __be32 tunnel_id_to_key(__be64 x)
-{
-#ifdef __BIG_ENDIAN
-	return (__force __be32)x;
-#else
-	return (__force __be32)((__force u64)x >> 32);
-#endif
-}
-
 static int __ipgre_rcv(struct sk_buff *skb, const struct tnl_ptk_info *tpi,
 		       struct ip_tunnel_net *itn, int hdr_len, bool raw_proto)
 {
@@ -290,7 +271,7 @@
 			__be64 tun_id;
 
 			flags = tpi->flags & (TUNNEL_CSUM | TUNNEL_KEY);
-			tun_id = key_to_tunnel_id(tpi->key);
+			tun_id = key32_to_tunnel_id(tpi->key);
 			tun_dst = ip_tun_rx_dst(skb, flags, tun_id, 0);
 			if (!tun_dst)
 				return PACKET_REJECT;
@@ -446,7 +427,7 @@
 
 	flags = tun_info->key.tun_flags & (TUNNEL_CSUM | TUNNEL_KEY);
 	gre_build_header(skb, tunnel_hlen, flags, proto,
-			 tunnel_id_to_key(tun_info->key.tun_id), 0);
+			 tunnel_id_to_key32(tun_info->key.tun_id), 0);
 
 	df = key->tun_flags & TUNNEL_DONT_FRAGMENT ?  htons(IP_DF) : 0;