Revert "ip6_vti: adjust vti mtu according to mtu of lower device"

This reverts commit 813b2da which is
commit 53c81e9 upstream.

Ben writes that there are a number of follow-on patches needed to fix
this up, but they get complex to backport, and some custom fixes are
needed, so let's just revert this and wait for a "real" set of patches
to resolve this to be submitted if it is really needed.

Reported-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Cc: Petr Vorel <pvorel@suse.cz>
Cc: Alexey Kodanev <alexey.kodanev@oracle.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

net/ipv6/ip6_vti.c

@@ -626,7 +626,6 @@ static void vti6_link_config(struct ip6_tnl *t)
 {
 	struct net_device *dev = t->dev;
 	struct __ip6_tnl_parm *p = &t->parms;
-	struct net_device *tdev = NULL;
 
 	memcpy(dev->dev_addr, &p->laddr, sizeof(struct in6_addr));
 	memcpy(dev->broadcast, &p->raddr, sizeof(struct in6_addr));
@@ -639,25 +638,6 @@ static void vti6_link_config(struct ip6_tnl *t)
 		dev->flags |= IFF_POINTOPOINT;
 	else
 		dev->flags &= ~IFF_POINTOPOINT;
-
-	if (p->flags & IP6_TNL_F_CAP_XMIT) {
-		int strict = (ipv6_addr_type(&p->raddr) &
-			      (IPV6_ADDR_MULTICAST | IPV6_ADDR_LINKLOCAL));
-		struct rt6_info *rt = rt6_lookup(t->net,
-						 &p->raddr, &p->laddr,
-						 p->link, strict);
-
-		if (rt)
-			tdev = rt->dst.dev;
-		ip6_rt_put(rt);
-	}
-
-	if (!tdev && p->link)
-		tdev = __dev_get_by_index(t->net, p->link);
-
-	if (tdev)
-		dev->mtu = max_t(int, tdev->mtu - dev->hard_header_len,
-				 IPV6_MIN_MTU);
 }
 
 /**