net: Drop CNodeRef for AttemptToEvictConnection

Locking for each operation here is unnecessary, and solves the wrong problem.
Additionally, it introduces a problem when cs_vNodes is held in an owning
class, to which invididual CNodeRefs won't have access.

These should be weak pointers anyway, once vNodes contain shared pointers.

Rather than using a refcounting class, use a 3-step process instead.

1. Lock vNodes long enough to snapshot the fields necessary for comparing
2. Unlock and do the comparison
3. Re-lock and mark the resulting node for disconnection if it still exists