IPv6: Fixed support for blackhole and prohibit routes

[ Upstream commit 7150aede5dd241539686e17d9592f5ebd28a2cda ]

The behaviour of blackhole and prohibit routes has been corrected by setting
the input and output pointers of the dst variable appropriately. For
blackhole routes, they are set to dst_discard and to ip6_pkt_discard and
ip6_pkt_discard_out respectively for prohibit routes.

ipv6: ip6_pkt_prohibit(_out) should not depend on
CONFIG_IPV6_MULTIPLE_TABLES

We need ip6_pkt_prohibit(_out) available without
CONFIG_IPV6_MULTIPLE_TABLES

Signed-off-by: Kamala R <kamala@aristanetworks.com>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>