Vlad says: The whole multiple cookie keys code is completely unused
and has been all this time. Noone uses anything other then the
secret_key[0] since there is no changeover support anywhere.

Thus, for now clean up its left-over fragments.

Cc: Neil Horman <nhorman@tuxdriver.com>
Cc: Vlad Yasevich <vyasevic@redhat.com>
Signed-off-by: NDaniel Borkmann <dborkman@redhat.com>
Acked-by: NNeil Horman <nhorman@tuxdriver.com>
Acked-by: NVlad Yasevich <vyasevich@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>