[FIB_TRIE]: Fix leaf freeing.

Seems like leaf (end-nodes) has been freed by __tnode_free_rcu and not
by __leaf_free_rcu. This fixes the problem. Only tnode_free is now
used which checks for appropriate node type. free_leaf can be removed.

Signed-off-by: Robert Olsson <robert.olsson@its.uu.se>
Signed-off-by: David S. Miller <davem@davemloft.net>