Ticket#576: Implement rest of the operate commands

Description:
 - First draft of the changes

Test Done:
 - Below ubus call tested
   ubus call usp get '{"path":"Device.WiFi.SSID.[BSSID==\"00:22:07:6D:5E:DD\"].SSID"}'
   ubus call usp get '{"path":"Device.IP.Interface.*.IPv4Address.*.IPAddress"}'
   ubus call usp get '{"path":"Device.WiFi.AccessPoint.[SSIDReference+BSSID==\"00:22:07:6D:5E:DD\"].SSID"}'
   ubus call usp set '{"path":"Device.WiFi.AccessPoint.[SSIDReference+BSSID==\"00:22:07:6D:5E:D\"].SSID", "value":"Test-2G"}'

Not Covered:
 - Operate command
 - Alias based addressing
 - Searching with List of References

usp/Makefile

@@ -0,0 +1,46 @@
+#
+# Copyright (C) 2019 Iopsys
+#
+
+include $(TOPDIR)/rules.mk
+
+PKG_NAME:=uspd
+PKG_VERSION:=1.0.0
+
+PKG_SOURCE_PROTO:=git
+PKG_SOURCE_VERSION:=e9aa8a42f1da90b44fbd6bca3f4131a24fe79efb
+PKG_SOURCE_URL:=https://dev.iopsys.eu/iopsys/uspd.git
+PKG_SOURCE:=$(PKG_NAME)-$(PKG_SOURCE_VERSION).tar.gz
+
+PKG_BUILD_DIR:=$(BUILD_DIR)/$(PKG_NAME)-$(PKG_VERSION)
+
+include $(INCLUDE_DIR)/package.mk
+
+define Package/uspd
+  SECTION:=utils
+  CATEGORY:=Utilities
+  TITLE:=TR069 extention for USP
+  DEPENDS:=+libubox +ubus +icwmp-curl
+endef
+
+define Package/uspd/description
+ Ubus based backend for TR-369/USP which can be used by other USP agents
+ running on top of it.
+endef
+
+TARGET_CFLAGS += \
+	-I$(STAGING_DIR)/usr/include \
+	-D_GNU_SOURCE
+
+#define Build/Prepare
+#        $(CP) -rf ./uspd/* $(PKG_BUILD_DIR)/
+#endef
+
+define Package/uspd/install
+	$(INSTALL_DIR) $(1)/etc/init.d
+	$(INSTALL_BIN) ./files/uspd.init $(1)/etc/init.d/uspd
+	$(INSTALL_DIR) $(1)/usr/sbin
+	$(INSTALL_BIN) $(PKG_BUILD_DIR)/uspd $(1)/usr/sbin/
+endef
+
+$(eval $(call BuildPackage,uspd))

usp/files/uspd.init

@@ -0,0 +1,19 @@
+#!/bin/sh /etc/rc.common
+
+START=94
+STOP=10
+
+USE_PROCD=1
+PROG=/usr/sbin/uspd
+
+start_service() {
+	procd_open_instance
+	procd_set_param command ${PROG}
+	procd_set_param respawn
+	procd_close_instance
+}
+
+reload_service() {
+	stop
+	start
+}