netifd: add a udhcpc.user placeholder script

Document the existence of this feature. This allows the user to execute a script
at each DHCPv4 event. This is useful, for example, as an ad-hoc way to update a
DDNS entry when (and only when) required.

Signed-off-by: Rui Salvaterra <rsalvaterra@gmail.com>

package/network/config/netifd/Makefile

@@ -1,7 +1,7 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=netifd
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_SOURCE_PROTO:=git
 PKG_SOURCE_URL=$(PROJECT_GIT)/project/netifd.git
@@ -25,6 +25,10 @@ define Package/netifd
   TITLE:=OpenWrt Network Interface Configuration Daemon
 endef
 
+define Package/netifd/conffiles
+/etc/udhcpc.user
+endef
+
 TARGET_CFLAGS += \
 	-I$(STAGING_DIR)/usr/include/libnl-tiny \
 	-I$(STAGING_DIR)/usr/include \

package/network/config/netifd/files/etc/udhcpc.user

@@ -0,0 +1 @@
+# This script is sourced by udhcpc's dhcp.script at every DHCP event.