Add option to enable flow control and pause metering 6.4.3

Pause metering allows the FortiSwitch to apply flow control to ingress traffic when the queue is congested, and to resume once it is cleared. In FortiOS, flow control and pause metering can be configured in the switch-controller managed-switch settings.

Parameter	Description
flow-control {disable | tx | rx | both}	Flow control direction. disable: Disable flow control. tx: Transmit pause control frames. rx: Receive pause control frames. both: Transmit and receive pause control frames.
pause-meter <integer>	Ingress metering rate in Kbps (128 – 2147483647, 0 = disable).
pause-meter-resume {75% | 50% | 25%}	Resume threshold for resuming traffic on the ingress port. The back pressure state will not be cleared until the bucket count falls below 75%, 50%, or 25% of the pause threshold.

To configure flow control and pause metering:

config switch-controller managed-switch
    edit "S248EPTF18000000"
        config ports
            edit "port6"
                set flow-control both
                set pause-meter 2000
                set pause-meter-resume 75%
            next
        end
    next
end