[barefoot]: Allow configuration of platform-specific interfaces used for internal purposes (#2631)

- Why it is required
since SONiC master switches ifupdown package to the new implementation (ifupdown2), it is required to change the configuration of a platform-specific interface for wedge100bf_32x and wedge100bf_65x platforms (bc of ifupdown2 doesn't support auto mode for inet6 protocol).

Also, need to make some refactoring and remove if platform == smth then.. from the system level scripts.

- What I did

removed customization of /usr/bin/interfaces-config.sh
explicitly created directory /etc/network/interfaces.d
added "source" to the /etc/network/interfaces generation template (to include platform-specific interfaces processing)
added platform-specific interfaces config itself (for wedge100bf_32x and wedge100bf_65x)
fixed testcase in sonic-config-engine
- How to verify it

build image for wedge100bf_32x
perform sudo config reload -y on new installation
check the correct configuration of usb0 interface
- Description for the changelog

Allow configuration of platform-specific interfaces

files/build_templates/sonic_debian_extension.j2

@@ -165,6 +165,7 @@ sudo cp $IMAGE_CONFIGS/interfaces/*.j2 $FILESYSTEM_ROOT_USR_SHARE_SONIC_TEMPLATE
 
 # Copy initial interfaces configuration file, will be overwritten on first boot
 sudo cp $IMAGE_CONFIGS/interfaces/init_interfaces $FILESYSTEM_ROOT/etc/network/interfaces
+sudo mkdir -p $FILESYSTEM_ROOT/etc/network/interfaces.d
 
 # Copy hostcfgd files
 sudo cp $IMAGE_CONFIGS/hostcfgd/hostcfgd.service $FILESYSTEM_ROOT/etc/systemd/system/

files/image_config/interfaces/interfaces-config.sh

@@ -4,18 +4,6 @@ ifdown --force eth0
 
 sonic-cfggen -d -t /usr/share/sonic/templates/interfaces.j2 > /etc/network/interfaces
 
-# Add usb0 interface for bfn platforms
-platform=$(sonic-cfggen -H -v 'DEVICE_METADATA["localhost"]["platform"]')
-if [[ "$platform" == "x86_64-accton_wedge100bf_32x-r0" || "$platform" == "x86_64-accton_wedge100bf_65x-r0" ]]; then
-cat <<'EOF' >> /etc/network/interfaces
-# BMC interface
-auto usb0
-allow-hotplug usb0
-iface usb0 inet6 auto
-up ifconfig usb0 txqueuelen 64
-EOF
-fi
-
 [ -f /var/run/dhclient.eth0.pid ] && kill `cat /var/run/dhclient.eth0.pid` && rm -f /var/run/dhclient.eth0.pid
 
 systemctl restart networking

files/image_config/interfaces/interfaces.j2

@@ -47,4 +47,6 @@ iface eth0 {{ 'inet' if prefix | ipv4 else 'inet6' }} static
 iface eth0 inet dhcp
 {% endif %}
 #
+source /etc/network/interfaces.d/*
+#
 {% endblock mgmt_interface %}

platform/barefoot/sonic-platform-modules-bfn-montara/configs/network/interfaces.d/usb0

@@ -0,0 +1,5 @@
+# BMC interface
+auto usb0
+allow-hotplug usb0
+iface usb0 inet6
+up ifconfig usb0 txqueuelen 64

platform/barefoot/sonic-platform-modules-bfn-montara/debian/rules

@@ -2,6 +2,7 @@
 
 PACKAGE_NAME := sonic-platform-modules-bfn-montara
 SCRIPT_SRC := $(shell pwd)/scripts
+CONFIGS_SRC := $(shell pwd)/configs
 
 %:
 	dh $@
@@ -9,6 +10,8 @@ SCRIPT_SRC := $(shell pwd)/scripts
 override_dh_auto_install:
 	dh_installdirs -p$(PACKAGE_NAME) usr/local/bin
 	cp -r $(SCRIPT_SRC)/* debian/$(PACKAGE_NAME)/usr/local/bin
+	dh_installdirs -p$(PACKAGE_NAME) etc/network/interfaces.d/
+	cp -r $(CONFIGS_SRC)/network/interfaces.d/* debian/$(PACKAGE_NAME)/etc/network/interfaces.d/
 
 override_dh_usrlocal:
 

platform/barefoot/sonic-platform-modules-bfn/configs/network/interfaces.d/usb0

@@ -0,0 +1,5 @@
+# BMC interface
+auto usb0
+allow-hotplug usb0
+iface usb0 inet6
+up ifconfig usb0 txqueuelen 64

platform/barefoot/sonic-platform-modules-bfn/debian/rules

@@ -2,6 +2,7 @@
 
 PACKAGE_NAME := sonic-platform-modules-bfn
 SCRIPT_SRC := $(shell pwd)/scripts
+CONFIGS_SRC := $(shell pwd)/configs
 
 %:
 	dh $@
@@ -9,6 +10,8 @@ SCRIPT_SRC := $(shell pwd)/scripts
 override_dh_auto_install:
 	dh_installdirs -p$(PACKAGE_NAME) usr/local/bin
 	cp -r $(SCRIPT_SRC)/* debian/$(PACKAGE_NAME)/usr/local/bin
+	dh_installdirs -p$(PACKAGE_NAME) etc/network/interfaces.d/
+	cp -r $(CONFIGS_SRC)/network/interfaces.d/* debian/$(PACKAGE_NAME)/etc/network/interfaces.d/
 
 override_dh_usrlocal:
 

src/sonic-config-engine/tests/sample_output/interfaces

@@ -47,4 +47,6 @@ iface eth0 inet6 static
     down ip -6 route delete 2603:10e2:0:2902::/64 dev eth0 table default
     down ip -6 rule delete from 2603:10e2:0:2902::8/128 table default
 #
+source /etc/network/interfaces.d/*
+#