patches crds vote-index assignment bug (#14438)

If tower is full, old votes are evicted from the front of the deque:
https://github.com/solana-labs/solana/blob/2074e407c/programs/vote/src/vote_state/mod.rs#L367-L373
whereas recent votes if expire are evicted from the back:
https://github.com/solana-labs/solana/blob/2074e407c/programs/vote/src/vote_state/mod.rs#L529-L537

As a result, from a single tower_index scalar, we cannot infer which crds-vote
should be overwritten:
https://github.com/solana-labs/solana/blob/2074e407c/core/src/crds_value.rs#L576

In addition there is an off by one bug in the existing code. tower_index is
bounded by MAX_LOCKOUT_HISTORY - 1:
https://github.com/solana-labs/solana/blob/2074e407c/core/src/consensus.rs#L382
So, it is at most 30, whereas MAX_VOTES is 32:
https://github.com/solana-labs/solana/blob/2074e407c/core/src/crds_value.rs#L29
Which means that this branch is never taken:
https://github.com/solana-labs/solana/blob/2074e407c/core/src/crds_value.rs#L590-L593
so crds table alwasys keeps 29 **oldest** votes by wallclock, and then
only overrides the 30st one each time. (i.e a tally of only two most
recent votes).

programs/vote/src/vote_state/mod.rs

@@ -429,6 +429,12 @@ impl VoteState {
         self.last_lockout().map(|v| v.slot)
     }
 
+    // Upto MAX_LOCKOUT_HISTORY many recent unexpired
+    // vote slots pushed onto the stack.
+    pub fn tower(&self) -> Vec<Slot> {
+        self.votes.iter().map(|v| v.slot).collect()
+    }
+
     fn current_epoch(&self) -> Epoch {
         if self.epoch_credits.is_empty() {
             0