Currently we can not flush cached pmtu/redirect informations via
the ipv4_sysctl_rtcache_flush sysctl. We need to check the rt_genid
of the old route and reset the nh exeption if the old route is
expired when we bind a new route to a nh exeption.
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>