Try to load system load averages from /proc/loadavg first. This should prevent reporting the load averages being too high on Proxmox LXC installations.

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What does this PR aim to accomplish?:

On Proxmox LXC installations the reported system load is the load of the host, not the LXC itself. This code change tries to retrieve the loads from /proc/loadavg first:

root@codedev:/home/pihole# cat loadavg.c 
#include <stdio.h>
#include <stdlib.h>

int getloadavg_proc(double * loadavg)
{
    FILE *f = fopen("/proc/loadavg", "r");
    if(f == NULL)
        return -1;

    int count = fscanf(f, "%lf %lf %lf", &loadavg[0], &loadavg[1], &loadavg[2]);
    fclose(f);
    if (count != 3)
        return -1;

    return 0;
}

int main() {
    double loadavg[3];

    if (getloadavg(loadavg, 3) == -1) {
        perror("Error getting sys load average");
        return 1;
    }

    printf("Sys load: %.2f %.2f %.2f\n", loadavg[0], loadavg[1], loadavg[2]);

    if (getloadavg_proc(loadavg) == -1) {
        perror("Error getting proc load average");
        return 1;
    }

    printf("Proc load: %.2f %.2f %.2f\n", loadavg[0], loadavg[1], loadavg[2]);
}

root@codedev:/home/pihole# ./loadavg 
Sys load: 2.66 2.85 2.70
Proc load: 0.00 0.00 0.00

To make sure the load averages make sense on Proxmox LXC installations, lxcfs on Proxmox should run with parameter --enable-loadavg.

How does this PR accomplish the above?:

Try to retreive the load averages from /proc/loadavg first. In case it fails, the old method (getloadavg) is used.

Link documentation PRs if any are needed to support this PR:

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