net/ipv6: stop leaking percpu memory in fib6 info

The fib6_info_alloc() function allocates percpu memory to hold per CPU
pointers to rt6_info, but this memory is never freed. Fix it.

Fixes: a64efe14

 ("net/ipv6: introduce fib6_info struct and helpers")
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>