When json flag is set do not print other than json

[vikumarks]

What I did

How I did it

How to verify it

admin@str-7060x6-64pe-stress-01:~$ portstat -i Ethernet0 -j -p 3
{
    "Ethernet0": {
        "RX_BPS": "0.00 B/s",
        "RX_DRP": "0",
        "RX_ERR": "0",
        "RX_OK": "0",
        "RX_OVR": "0",
        "RX_UTIL": "0.00%",
        "STATE": "U",
        "TX_BPS": "17.12 B/s",
        "TX_DRP": "0",
        "TX_ERR": "0",
        "TX_OK": "0",
        "TX_OVR": "0",
        "TX_UTIL": "0.00%"
    }
}
admin@str-7060x6-64pe-stress-01:~$ portstat -i Ethernet0 -p 3
The rates are calculated within 3 seconds period       <----------------------------
    IFACE    STATE    RX_OK    RX_BPS    RX_UTIL    RX_ERR    RX_DRP    RX_OVR    TX_OK     TX_BPS    TX_UTIL    TX_ERR    TX_DRP    TX_OVR
---------  -------  -------  --------  ---------  --------  --------  --------  -------  ---------  ---------  --------  --------  --------
Ethernet0        U        0  0.00 B/s      0.00%         0         0         0        6  12.92 B/s      0.00%         0         0         0

Previous command output (if the output of a command-line utility has changed)

admin@str-7060x6-64pe-stress-01:~$ portstat -i Ethernet0 -p 3 -j
The rates are calculated within 3 seconds period
{
    "Ethernet0": {
        "RX_BPS": "0.00 B/s",
        "RX_DRP": "0",
        "RX_ERR": "0",
        "RX_OK": "0",
        "RX_OVR": "0",
        "RX_UTIL": "0.00%",
        "STATE": "U",
        "TX_BPS": "1.69 B/s",
        "TX_DRP": "0",
        "TX_ERR": "0",
        "TX_OK": "0",
        "TX_OVR": "0",
        "TX_UTIL": "0.00%"
    }
}

New command output (if the output of a command-line utility has changed)

admin@str-7060x6-64pe-stress-01:~$ portstat -i Ethernet0 -p 3 -j
{
    "Ethernet0": {
        "RX_BPS": "0.00 B/s",
        "RX_DRP": "0",
        "RX_ERR": "0",
        "RX_OK": "0",
        "RX_OVR": "0",
        "RX_UTIL": "0.00%",
        "STATE": "U",
        "TX_BPS": "4.79 B/s",
        "TX_DRP": "0",
        "TX_ERR": "0",
        "TX_OK": "0",
        "TX_OVR": "0",
        "TX_UTIL": "0.00%"
    }
}

[mssonicbld]

/azp run

[azure-pipelines]

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