Fix: improve timestamp calculation for st20 st40 st41

[tszumski]

Improve timestamp calculation for st20 st40 st41, based on #1213

Fixes #1211

[DawidWesierski4]

This doesn't seem to be complient with video

[DawidWesierski4]

Tried a few times cannot achive compliaency with this patch need some more work

[DawidWesierski4]

Doesn't achive compliance with
Base one works fine
#1230

{
    "interfaces": [
        {
            "name": "0000:4b:01.0",
            "ip": "192.168.0.1"
        },
        {
            "name": "0000:4b:11.1",
            "ip": "192.168.0.2"
        }
    ],
    "tx_sessions": [
        {
            "dip": [
                "239.168.75.30",
                "239.168.75.31"
            ],
            "interface": [
                0,
                1
            ],
            "st20p": [
                {
                    "replicas": 1,
                    "start_port": 20000,
                    "payload_type": 112,
                    "width": 1920,
                    "height": 1080,
                    "fps": "p60",
                    "device": "AUTO",
                    "input_format": "YUV422PLANAR10LE",
                    "transport_format": "YUV_422_10bit",
                    "st20p_url": "/mnt/ramdisk/file.yuv",
                    "user_pacing": true
                }
            ],
            "st30p": [
                {
                    "replicas": 1,
                    "start_port": 30000,
                    "payload_type": 111,
                    "audio_format": "PCM24",
                    "audio_channel": ["U02"],
                    "audio_sampling": "48kHz",
                    "audio_ptime": "1",
                    "audio_url": "/mnt/ramdisk/file.yuv",
                    "user_pacing": true
                }
            ],
            "user_pacing_offset" : 130000000
        }
    ]
}