fib_info can be shared by many route prefixes but we don't want
duplicate alternative routes for a prefix+tos+priority. Last change
was not correct to check fib_treeref because it accounts usage from
other prefixes. Additionally, avoid replacement without error if new
route is same, as Joonwoo Park suggests.
Signed-off-by: NJulian Anastasov <ja@ssi.bg>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>