Some NSCs have more routes than expected after node restart

[NikitaSkrynnik]

Description

After node restart some of the NSCs have more routes than expected. Only one of them is pingable. Here is the example of routes after serveral node restarts:

default via 10.244.2.1 dev eth0 
10.244.2.0/24 via 10.244.2.1 dev eth0  src 10.244.2.12 
10.244.2.1 dev eth0 scope link  src 10.244.2.12 
172.16.0.34 dev nsm-v4 
172.16.0.40 dev nsm-v4 
172.16.0.56 dev nsm-v4 
172.16.0.92 dev nsm-v4 

Possible solution

Cleanup ip_context in case of reselect state on NSC

[denis-tingaikin]

/cc @szvincze @ljkiraly @edwarnicke

[NikitaSkrynnik]

@edwarnicke @szvincze what do you think about creating an endpoint with more strict policies that deletes suspicious routes from ip_context?