net/ipv4: Remove fib table id from rtable

Remove rt_table_id from rtable. It was added for getroute to return the
table id that was hit in the lookup. With the changes for fibmatch the
table id can be extracted from the fib_info returned in the fib_result
so it no longer needs to be in rtable directly.

Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>