raft: next index shall be larger than match index.

[wego1236]

Leader shall always replicate its log from a index larger than corresponding match index. Note that this is not a correctness issue, but rather an optimization in case of message reordering.

Related: #555

[ti-chi-bot]

Thanks for your pull request. Before we can look at it, you'll need to add a 'DCO signoff' to your commits.

📝 Please follow instructions in the contributing guide to update your commits with the DCO

Full details of the Developer Certificate of Origin can be found at developercertificate.org.

The list of commits missing DCO signoff:

• d477765 push raft-rs into project
• 1fcd501 modify file struct, add UDP tla
• f1676e9 Merge branch 'tikv:master' into master
• 413da20 Fixed a case in progress.go maybe_decr_to that could cause the next value to be less than or equal to the match value in the probe state

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository. I understand the commands that are listed here.