net: Set rtm_table to RT_TABLE_COMPAT for ipv6 for tables > 255

BugLink: https://bugs.launchpad.net/bugs/1822271

[ Upstream commit 97f0082a ]

Set rtm_table to RT_TABLE_COMPAT for ipv6 for tables > 255 to
keep legacy software happy. This is similar to what was done for
ipv4 in commit 709772e6 ("net: Fix routing tables with
id > 255 for legacy software").
Signed-off-by: Kalash Nainwal <kalash@arista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Juerg Haefliger <juerg.haefliger@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

net/ipv6/route.c

@@ -3117,7 +3117,7 @@ static int rt6_fill_node(struct net *net,
 		table = rt->rt6i_table->tb6_id;
 	else
 		table = RT6_TABLE_UNSPEC;
-	rtm->rtm_table = table;
+	rtm->rtm_table = table < 256 ? table : RT_TABLE_COMPAT;
 	if (nla_put_u32(skb, RTA_TABLE, table))
 		goto nla_put_failure;
 	if (rt->rt6i_flags & RTF_REJECT) {