filter the duplicated route add

[steven_chen3_dell.com]

Summary

If duplicate adding route table, the route nhop entry is set to multipath entry.
I think that is not a good idea, and it's better to add route as single path if the route hasn't more than one real path.

[zlei]

@steven_chen3_dell.com

I'm not getting you the 'duplicate adding route table'.

What is the behavior you expect?

[steven_chen3_dell.com]

@zlei
There are two same default route tables in my system , and both default route tables only have "Flags" difference(one is UG, another is UGS).
The kernel self cannot guarantee that routes will not be added repeatedly, maybe dhcp client or other user application add the same route entry.