ipv6: Fix tcp socket connection with DSCP.

stable inclusion
from stable-v5.10.169
commit 7546fb3554df580e49b490c21a61dd3c38212571
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7V9QX

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7546fb3554df580e49b490c21a61dd3c38212571



----------------------------------------------------

commit 8230680f upstream.

Take into account the IPV6_TCLASS socket option (DSCP) in
tcp_v6_connect(). Otherwise fib6_rule_match() can't properly
match the DSCP value, resulting in invalid route lookup.

For example:

  ip route add unreachable table main 2001:db8::10/124

  ip route add table 100 2001:db8::10/124 dev eth0
  ip -6 rule add dsfield 0x04 table 100

  echo test | socat - TCP6:[2001:db8::11]:54321,ipv6-tclass=0x04

Without this patch, socat fails at connect() time ("No route to host")
because the fib-rule doesn't jump to table 100 and the lookup ends up
being done in the main table.

Fixes: 2cc67cc7 ("[IPV6] ROUTE: Routing by Traffic Class.")
Signed-off-by: Guillaume Nault <gnault@redhat.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: zhaoxiaoqiang11 <zhaoxiaoqiang11@jd.com>