Threshold update should increase sequence number

[CanardMandarin]

The threshold update should invalidate previously created transactions.
Note: This change will increment the seq two times when calling set_owners_and_change_threshold.

[callensm]

the owner_set_seq value is to track the current numerical sequence number of the set of owner public keys. since updating the threshold doesn't have any change implications to the owner public keys, this value should not be incremented.