Implement IP netmask calculation to replace "ipcalc -m"
    
    Resolves: bz1947347
    Upstream: Fedora
    Conflict: None
    
    commit 1ca1b71780b83aa7ede1246d435c9a4207473a3b
    Author: Coiby Xu <coxu@redhat.com>
    Date:   Thu Apr 8 11:44:26 2021 +0800
    
        Implement IP netmask calculation to replace "ipcalc -m"
    
        Recently, dracut-network drops depedency on dhcp-client which requires
        ipcalc. Thus the dependency chain
        "kexec-tools -> dracut-network -> dhcp-client -> ipcalc"
        is broken. When NIC is configured to a static IP, kexec-tools depended
        on "ipcalc -m" to get netmask. This commit implements the shell
        equivalent of "ipcalc -m".
    
        The following test code shows cal_netmask_by_prefix is consistent with
        "ipcalc -m",
    
            #!/bin/bash
            . dracut-module-setup.sh
    
            for i in {0..128}; do
                mask_expected=$(ipcalc -m fe::/$i| cut -d"=" -f2)
                mask_actual=$(cal_netmask_by_prefix $i "-6")
                if [[ "$mask_expected" != "$mask_actual" ]]; then
                    echo "prefix="$i, "expected="$mask_expected, "acutal="$mask_actual
                    exit
                fi
            done
    
            echo "IPv6 tests passed"
    
            for i in {0..32}; do
                mask_expected=$(ipcalc -m 8.8.8.8/$i| cut -d"=" -f2)
                mask_actual=$(cal_netmask_by_prefix $i "")
                if [[ "$mask_expected" != "$mask_actual" ]]; then
                    echo "prefix="$i, "expected="$mask_expected, "acutal="$mask_actual
                    exit
                fi
            done
    
            echo "IPv4 tests passed"
    
            i=-2
            res=$(cal_netmask_by_prefix "$i" "")
            if [[ $? -ne 1 ]]; then
                echo "cal_netmask_by_prefix should exit when prefix<0"
                exit
            fi
    
            res=$(cal_netmask_by_prefix "$i" "")
            if [[ $? -ne 1 ]]; then
                echo "cal_netmask_by_prefix should exit when prefix<0"
                exit
            fi
    
            i=33
            $(cal_netmask_by_prefix $i "")
            if [[ $? -ne 1 ]]; then
                echo "cal_netmask_by_prefix should exit when prefix>32 for IPv4"
                exit
            fi
    
            i=129
            $(cal_netmask_by_prefix $i "-6")
            if [[ $? -ne 1 ]]; then
                echo "cal_netmask_by_prefix should exit when prefix>128 for IPv4"
                exit
            fi
    
            echo "Bad prefixes tests passed"
    
            echo "All tests passed"
    
        Reported-by: Jie Li <jieli@redhat.com>
        Signed-off-by: Coiby Xu <coxu@redhat.com>
        Acked-by: Kairui Song <kasong@redhat.com>
    
    Signed-off-by: Coiby Xu <coxu@redhat.com>