Add a parameter to specify the socket priority to txrx-tsn

The vlan-prio command line option is used to specify the PCP value and the socket priority:

    {"vlan-prio",   'q',    "NUM",  0, "packet vlan priority, also socket priority\n"
                       "    Def: 0 | Min: 0 | Max: 7"},

The value supplied, between 0 and 7, is then used to:

Set the socket prio
Set the XDP queue to be used
Set the PCP value

    case 'q':
        len = strlen(arg);
        res = strtol((const char *)arg, &str_end, 10);
        if (errno || res < 0 || res >= 7 || str_end != &arg[len])
            exit_with_error("Invalid queue number/socket priority. Check --help");
        opt->socket_prio = (uint32_t)res;
#ifdef WITH_XDP
        opt->x_opt.queue = opt->socket_prio;
#endif
        opt->vlan_prio = opt->socket_prio * 32;
        break;

Implementation suggestion

The implementation would require to parse a new option for 'socket-prio'. The behavior would be as follows:

AF_PACKET (socket mode afpkt parameter)
- Only vlan-prio is provided: same behavior as of now, to keep backwards compatibility.
- Only socket-prio is provided
- Check that the value is in the 0 to 15 range
- Initialize opt->socket_prio to the value provided for the parameter
- Leave opt->vlan_prio with the default value
- Both are provided: vlan-prio is configured first as when only vlan-prio is provided. Then, on top of it, apply the socket-prio configuration as above: check that the value is in the 0-15 range, and then initialize opt->socket_prio to the value provided for the parameter. opt->vlan_prio remains with the value provided for the vlan-prio parameter.
AF_XDP (socket mode afxdp parameter)
- Only vlan-prio is provided: same behavior as of now, to keep backwards compatibility.
- Only socket-prio is provided: raise an error and inform that AF_XDP sockets do not implement a socket priority
- Both are provided: raise an error and inform that AF_XDP sockets do not implement a socket priority

@AzuraTarmiziIntel could you please provide some guidance about how to proceed with this usage of socket_prio?

intel / iotg_tsn_ref_sw

Add a parameter to specify the socket priority to txrx-tsn #30

Implementation suggestion