Support validator vote only mode

[mmcgee-jump]

Just need to drop packets at TPU arrival time if in vote only mode

[ptaffet-jump]

Logic for entering/exiting vote only mode:
https://github.com/anza-xyz/agave/blob/bb70670048f589264f83111a4fdb4972eea18a41/core/src/replay_stage.rs#L1258-L1291