[PATCH ipsec-next] ip6_vti: use IS_REACHABLE to avoid some compile errors

[Xin Long]

Naresh reported some compile errors:

  arm build failed due this error on linux-next 20200713 and  20200713
  net/ipv6/ip6_vti.o: In function `vti6_rcv_tunnel':
  ip6_vti.c:(.text+0x1d20): undefined reference to `xfrm6_tunnel_spi_lookup'

This happened when set CONFIG_IPV6_VTI=y and CONFIG_INET6_TUNNEL=m.
We don't really want ip6_vti to depend inet6_tunnel completely, but
only to disable the tunnel code when inet6_tunnel is not seen.

So instead of adding "select INET6_TUNNEL" for IPV6_VTI, this patch
is only to change to IS_REACHABLE to avoid these compile error.

Reported-by: Naresh Kamboju <naresh.kamb...@linaro.org>
Fixes: 08622869ed3f ("ip6_vti: support IP6IP6 tunnel processing with 
.cb_handler")
Signed-off-by: Xin Long <lucien....@gmail.com>
---
 net/ipv6/ip6_vti.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/ipv6/ip6_vti.c b/net/ipv6/ip6_vti.c
index 18ec4ab..53f12b4 100644
--- a/net/ipv6/ip6_vti.c
+++ b/net/ipv6/ip6_vti.c
@@ -1218,7 +1218,7 @@ static struct xfrm6_protocol vti_ipcomp6_protocol 
__read_mostly = {
        .priority       =       100,
 };
 
-#if IS_ENABLED(CONFIG_INET6_XFRM_TUNNEL)
+#if IS_REACHABLE(CONFIG_INET6_XFRM_TUNNEL)
 static int vti6_rcv_tunnel(struct sk_buff *skb)
 {
        const xfrm_address_t *saddr;
@@ -1270,7 +1270,7 @@ static int __init vti6_tunnel_init(void)
        err = xfrm6_protocol_register(&vti_ipcomp6_protocol, IPPROTO_COMP);
        if (err < 0)
                goto xfrm_proto_comp_failed;
-#if IS_ENABLED(CONFIG_INET6_XFRM_TUNNEL)
+#if IS_REACHABLE(CONFIG_INET6_XFRM_TUNNEL)
        msg = "ipv6 tunnel";
        err = xfrm6_tunnel_register(&vti_ipv6_handler, AF_INET6);
        if (err < 0)
@@ -1288,7 +1288,7 @@ static int __init vti6_tunnel_init(void)
        return 0;
 
 rtnl_link_failed:
-#if IS_ENABLED(CONFIG_INET6_XFRM_TUNNEL)
+#if IS_REACHABLE(CONFIG_INET6_XFRM_TUNNEL)
        err = xfrm6_tunnel_deregister(&vti_ip6ip_handler, AF_INET);
 vti_tunnel_ip6ip_failed:
        err = xfrm6_tunnel_deregister(&vti_ipv6_handler, AF_INET6);
@@ -1312,7 +1312,7 @@ static int __init vti6_tunnel_init(void)
 static void __exit vti6_tunnel_cleanup(void)
 {
        rtnl_link_unregister(&vti6_link_ops);
-#if IS_ENABLED(CONFIG_INET6_XFRM_TUNNEL)
+#if IS_REACHABLE(CONFIG_INET6_XFRM_TUNNEL)
        xfrm6_tunnel_deregister(&vti_ip6ip_handler, AF_INET);
        xfrm6_tunnel_deregister(&vti_ipv6_handler, AF_INET6);
 #endif
-- 
2.1.0