Longest prefix match

[mikma]

Sort the route table in descending sort order based on the prefix length. This way finding the route in the route table will result in longest prefix match, as is expected.

Fixes #1769

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[mikma]

@googlebot I fixed it.

[mikma]

I'm having problem understanding why subnet masks which aren't in the canonical form (i.e they don't represent a CIDR prefix) are allowed in the tcpip package. I don't think it makes sense to add routes to such subnets/prefixes to the route table.

My proposition is to require that subnet masks must be in canonical form, and I have added a verification to tcpip.NewSubnet in a separate commit together with updated test cases.

[mikma]

I updated the branch with a new version which doesn't change NewSubnet, but instead validates the routes in SetRouteTable, and AddRoute.

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[github-actions[bot]]

This PR has been closed due to lack of activity.