scsi: lpfc: Zero CGN stats only during initial driver load and stat reset

Currently congestion management framework results are cleared whenever the
framework settings changed (such as it being turned off then back on). This
unfortunately means prior stats, rolled up to higher time windows lose
meaning.

Change such that stats are not cleared. Thus they pause and resume with
prior values still being considered.

Link: https://lore.kernel.org/r/20210910233159.115896-13-jsmart2021@gmail.com


Co-developed-by: Justin Tee <justin.tee@broadcom.com>
Signed-off-by: Justin Tee <justin.tee@broadcom.com>
Signed-off-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>