Add missing readlink required for iptables-nft(post)
    
    The following is observed while creating fedora-server image:
      Running scriptlet: iptables-nft-1.8.5-5.fc33.armv7hl
    /var/tmp/rpm-tmp.5nTAii: line 14: readlink: command not found
    /var/tmp/rpm-tmp.5nTAii: line 14: readlink: command not found
    /var/tmp/rpm-tmp.5nTAii: line 18: readlink: command not found
    /var/tmp/rpm-tmp.5nTAii: line 31: readlink: command not found
    /var/tmp/rpm-tmp.5nTAii: line 34: readlink: command not found
    /var/tmp/rpm-tmp.5nTAii: line 31: readlink: command not found
    /var/tmp/rpm-tmp.5nTAii: line 34: readlink: command not found
    /var/tmp/rpm-tmp.5nTAii: line 31: readlink: command not found
    /var/tmp/rpm-tmp.5nTAii: line 34: readlink: command not found
    /var/tmp/rpm-tmp.5nTAii: line 38: readlink: command not found