Wallet: Fix JavaDoc for setKeyRotationTime() and accept null argument to stop key rotation.
Wallet: Fix JavaDoc for setKeyRotationTime() and accept null argument to stop key rotation.

(cherry picked from commit 3fea6428ef7f496f4b816453bf611668cb521705)
Signed-off-by: HashEngineering <cdfd0e2929fd184ec34228d20f211727fcb487d4@gmail.com>

HashEngineering/dashj,HashEngineering/darkcoinj,HashEngineering/darkcoinj,HashEngineering/dashj,HashEngineering/dashj,HashEngineering/dashj,HashEngineering/darkcoinj