Defrag unsets backend options

[lavacat]

What happened?

After running defrag backend options will be unset. For example FreelistType will be ""

What did you expect to happen?

Defrag should preserve original backend options

How can we reproduce it (as minimally and precisely as possible)?

See unit test in PR.

Anything else we need to know?

No response

Etcd version (please run commands below)

affects 3.5 and 3.4 releases

Etcd configuration (command line flags or environment variables)

paste your configuration here

Etcd debug information (please run commands blow, feel free to obfuscate the IP address or FQDN in the output)

$ etcdctl member list -w table
# paste output here

$ etcdctl --endpoints=<member list> endpoint status -w table
# paste output here

Relevant log output

No response

[serathius]

Thanks for sending PR, can you create a backport PRs to 3.5 and 3.4 after merge?

[lavacat]

Thanks for sending PR, can you create a backport PRs to 3.5 and 3.4 after merge?

Yes, I'll submit similar PRs for 3.5 and 3.4