fix(core): small logic bugs

[encodeous]

1. Seqno requests should not be forwarded to the node that sent it
2. We should recompute routes after handling a neighbour update
3. Edge case where equal-metric routes can be unstable, depending on internal ordering
4. Held routes are not properly blackholed
5. isSelected does not check source (source could have changed)
6. Inactive endpoints are not checked properly when making routing decisions
7. Retracted routes should not update feasibility distance