[IPV4] fib_trie: fix proc interface

Create one iterator for walking over FIB trie, and use it
for all the /proc functions. Add a /proc/net/route
output for backwards compatibility with old applications.

Make initialization of fib_trie same as fib_hash so no #ifdef
is needed in af_inet.c

Fixes: http://bugzilla.kernel.org/show_bug.cgi?id=5209



Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>