include/kernel.mk: build kmod packages with empty FILES

kmod packages without FILES did not have an install step defined, leading
to no package being built. This affected netfilter/iptables packages, which
filter out builtin modules from FILES.

Not building a package that it is selected in .config is problematic, as
the generated empty package may be necessary to satisfy dependencies.

Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>

include/kernel.mk

@@ -225,8 +225,7 @@ $(call KernelPackage/$(1)/config)
   $(call KernelPackage/hooks)
 
   ifneq ($(if $(filter-out %=y %=n %=m,$(KCONFIG)),$(filter m y,$(foreach c,$(filter-out %=y %=n %=m,$(KCONFIG)),$($(c)))),.),)
-    ifneq ($(strip $(FILES)),)
+    define Package/kmod-$(1)/install
-      define Package/kmod-$(1)/install
 		  @for mod in $$(call version_filter,$$(FILES)); do \
 			if grep -q "$$$$$$$${mod##$(LINUX_DIR)/}" "$(LINUX_DIR)/modules.builtin"; then \
 				echo "NOTICE: module '$$$$$$$$mod' is built-in."; \
@@ -240,8 +239,7 @@ $(call KernelPackage/$(1)/config)
 		  done;
 		  $(call ModuleAutoLoad,$(1),$$(1),$(filter-out 0-,$(word 1,$(AUTOLOAD))-),$(filter-out 0,$(word 2,$(AUTOLOAD))),$(wordlist 3,99,$(AUTOLOAD)))
 		  $(call KernelPackage/$(1)/install,$$(1))
-      endef
+    endef
-    endif
   $(if $(CONFIG_PACKAGE_kmod-$(1)),
     else
       compile: $(1)-disabled