package/ifupdown-scripts: do not expect localhost to precede DHCP

Currently, we always suppose that localhost settings will always come
before the (optional) DHCP ones. This is always true when using
sysvinit/busybox or systemd.

However, with openrc, this will no longer be the case: only the DHCP
settings will be present (OpenRC handles lo on his own).

So, prepare the macros to be independent one from the other, and for
symetry, in both:
  - use append-redirection >> to populate the interfaces file,
  - prepend a leading empty line at the beginning of each section.

The origianl singe '>' redirection would ensure the file would not grow
on a reinstall, but that's no longer the case, so reset the file prior
to filling it, using the canned preamble.

Signed-off-by: Carlos Santos <unixmania@gmail.com>
[yann.morin.1998@free.fr: split off to its own patch]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/ifupdown-scripts/ifupdown-scripts.mk

@@ -4,13 +4,17 @@
 #
 ################################################################################
 
+define IFUPDOWN_SCRIPTS_PREAMBLE
+	echo "# interface file auto-generated by buildroot" \
+		> $(TARGET_DIR)/etc/network/interfaces
+endef
+
 define IFUPDOWN_SCRIPTS_LOCALHOST
 	( \
-		echo "# interface file auto-generated by buildroot"; \
 		echo ; \
 		echo "auto lo"; \
 		echo "iface lo inet loopback"; \
-	) > $(TARGET_DIR)/etc/network/interfaces
+	) >> $(TARGET_DIR)/etc/network/interfaces
 endef
 
 IFUPDOWN_SCRIPTS_DHCP_IFACE = $(call qstrip,$(BR2_SYSTEM_DHCP))
@@ -37,6 +41,7 @@ endef
 define IFUPDOWN_SCRIPTS_INSTALL_INIT_SYSV
 	$(INSTALL) -D -m 0755 $(IFUPDOWN_SCRIPTS_PKGDIR)/S40network \
 		$(TARGET_DIR)/etc/init.d/S40network
+	$(IFUPDOWN_SCRIPTS_PREAMBLE)
 	$(IFUPDOWN_SCRIPTS_LOCALHOST)
 	$(IFUPDOWN_SCRIPTS_DHCP)
 endef
@@ -47,6 +52,7 @@ endef
 define IFUPDOWN_SCRIPTS_INSTALL_INIT_SYSTEMD
 	$(INSTALL) -D -m 644 $(IFUPDOWN_SCRIPTS_PKGDIR)/network.service \
 		$(TARGET_DIR)/etc/systemd/system/network.service
+	$(IFUPDOWN_SCRIPTS_PREAMBLE)
 	$(IFUPDOWN_SCRIPTS_LOCALHOST)
 	$(IFUPDOWN_SCRIPTS_DHCP)
 endef