feat: Check network interface (#513)

update-alternatives --set iptables /usr/sbin/iptables-legacy > /dev/null

update-alternatives --set ip6tables /usr/sbin/ip6tables-legacy > /dev/null

if [ ! -d "/sys/class/net/$VM_NET_DEV" ]; then

  error "Network interface $VM_NET_DEV does not exist inside the container!"

  error "$ADD_ERR -e \"VM_NET_DEV=NAME\" to specify another interface name." && exit 27

fi

VM_NET_MAC="${VM_NET_MAC//-/:}"

GATEWAY=$(ip r | grep default | awk '{print $3}')

IP=$(ip address show dev "$VM_NET_DEV" | grep inet | awk '/inet / { print $2 }' | cut -f1 -d/)