ipv4: Fix fib_info->fib_metrics leak

Commit 4670994d(net,rcu: convert call_rcu(fc_rport_free_rcu) to
kfree_rcu()) introduced a memory leak. This patch reverts it.

Signed-off-by: Zheng Yan <zheng.z.yan@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>