Removed duplicate function install grub and set GRUB_CMDLINE_LINUX

[GermanAizek]

@Ysurac,
while I was adding ability to use u-boot, I noticed repetition code due to inattention

openmptcprouter-vps/debian9-x86_64.sh

Lines 358 to 379 in c0c9627

	if [ -z "$(dpkg-query -l | grep grub)" ]; then
	if [ -d /boot/grub2 ]; then
	apt-get -y install grub2
	elif [ -d /boot/grub ]; then
	apt-get -y install grub-legacy
	fi
	[ -n "$(grep 'net.ifnames=0' /boot/grub/grub.cfg)" ] && [ ! -f /etc/default/grub ] && {
	echo 'GRUB_CMDLINE_LINUX="net.ifnames=0 biosdevname=0"' > /etc/default/grub
	}
	fi
	if [ -z "$(dpkg-query -l | grep grub)" ]; then
	if [ -d /boot/grub2 ]; then
	apt-get -y install grub2
	elif [ -d /boot/grub ]; then
	apt-get -y install grub-legacy
	fi
	[ -n "$(grep 'net.ifnames=0' /boot/grub/grub.cfg)" ] && [ ! -f /etc/default/grub ] && {
	echo 'GRUB_CMDLINE_LINUX="net.ifnames=0 biosdevname=0"' > /etc/default/grub
	}
	fi