cpus_allowed: use __NRPROCESSORS_CONF instead of __SC_NPROCESSORS_ONLN for non-sequen...

cpus_allowed: use __NRPROCESSORS_CONF instead of __SC_NPROCESSORS_ONLN for non-sequential CPU ids

When disabling SMT on some systems, the ID of some available CPU may
be larger than the value of sysconf(_SC_NPROCESSORS_ONLN). Without
this patch, fio complains that the expected CPU ID is invalid. Here's
an example from my server:

    $ ./fio --cpus_allowed=14 --ioengine=libaio --direct=1 --name=test --numjobs=1 --blocksize=128k --iodepth=1 --rw=read --filename=/dev/nvme0n1
    fio: CPU 14 too large (max=11)
    fio: failed parsing cpus_allowed=14

System information:

    $ lscpu
    Architecture:         x86_64
    CPU op-mode(s):       32-bit, 64-bit
    Byte Order:           Little Endian
    CPU(s):               20
    On-line CPU(s) list:  0,2,4,6,8,10,12,14,16-19
    Off-line CPU(s) list: 1,3,5,7,9,11,13,15
    ...
    Model name:           12th Gen Intel(R) Core(TM) i7-12700
    BIOS Model name:      12th Gen Intel(R) Core(TM) i7-12700
    ...

    $ uname -a
    Linux localhost.localdomain 4.18.0-348.el8.x86_64 #1 SMP Tue Oct 19 15:14:17 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

    $ cat /etc/redhat-release
    CentOS Linux release 8.5.2111

    $ cat /proc/cmdline
    BOOT_IMAGE=(hd0,gpt2)/vmlinuz-4.18.0-348.el8.x86_64 root=/dev/mapper/cl-root ro nosmt isolcpus=0,2,4,6,8,10,12,14 crashkernel=auto resume=/dev/mapper/cl-swap rd.lvm.lv=cl/root rd.lvm.lv=cl/swap rhgb quiet

    $ cat test.c
    #include <stdio.h>
    #include <unistd.h>
    int main(int argc, char *argv[])
    {
        printf("_SC_NPROCESSORS_ONLN=%ld _SC_NPROCESSORS_CONF=%ld\n",
               sysconf(_SC_NPROCESSORS_ONLN), sysconf(_SC_NPROCESSORS_CONF));
    }

    $ gcc test.c

    $ ./a.out
    _SC_NPROCESSORS_ONLN=12 _SC_NPROCESSORS_CONF=20

Signed-off-by: mayuanpeng <mayuanpeng@dapustor.com>