Only create new slashing period when validator is unjailed, not re-enters validator set

[sunnya97]

From #3103:

Currently, according to the slashing module spec, a new slashing period is created everytime a validator is unbonded then rebonded. This should probably be changed to jailed/unjailed, as in the current system, let's say I compromised the key of the rank 100 validator, I could bond my own validator into and out of the validator set many times, in order to create as many slashing periods I want for the validator. Then I can create infractions for each of the slashing periods I created for the validator, allowing me to get them multiply slashed. I'm not sure if this is how it is implemented in the code, or is just a mistake in the spec.

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[sunnya97]

This was closed by #3225.