sdk: bundle usbip userspace sources

Bundle the usbip utility sources shipped with the Linux kernel tree in
order to allow the usbip packages from the package feed to build within
the OpenWrt SDK.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

target/sdk/Makefile

@@ -84,6 +84,10 @@ $(BIN_DIR)/$(SDK_NAME).tar.xz: clean
 		$(SDK_DIRS) $(KERNEL_FILES) | \
 		$(TAR) -xf - -C $(SDK_BUILD_DIR)
 
+	# Copy usbip sources, this is required for the usbip userspace packages to be buildable by the SDK.
+	$(TAR) -cf - -C $(TOPDIR) $(KDIR_BASE)/tools/usb/usbip/ | \
+		$(TAR) -xf - -C $(SDK_BUILD_DIR)
+
 	(cd $(SDK_BUILD_DIR); find $(STAGING_SUBDIR_HOST)/bin $(STAGING_SUBDIR_HOST)/usr/bin \
 		$(STAGING_SUBDIR_TOOLCHAIN)/bin $(STAGING_SUBDIR_TOOLCHAIN)/*/bin $(STAGING_SUBDIR_TOOLCHAIN)/libexec \
 		-type f | $(XARGS) $(SCRIPT_DIR)/bundle-libraries.sh $(SDK_BUILD_DIR)/$(STAGING_SUBDIR_HOST))