net/ipv6: Remove unnecessary clean.

The route here is newly created. It is unnecessary to call
fib6_clean_expires() on it.

Suggested-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>