nvmet: reset keep alive timer in controller enable

[ Upstream commit d68a90e148f5a82aa67654c5012071e31c0e4baa ]

Controllers that are not yet enabled should not really enforce keep alive
timeouts, but we still want to track a timeout and cleanup in case a host
died before it enabled the controller.  Hence, simply reset the keep
alive timer when the controller is enabled.

Suggested-by: Max Gurtovoy <maxg@mellanox.com>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>