ebpf: Add a separate target for skeleton

This generalizes the rule to generate the skeleton and allows to add
another.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

tools/ebpf/Makefile.ebpf

@@ -1,23 +1,24 @@
-OBJS = rss.bpf.o
+SKELETONS = rss.bpf.skeleton.h
 
 LLVM_STRIP ?= llvm-strip
 CLANG ?= clang
 INC_FLAGS = `$(CLANG) -print-file-name=include`
 EXTRA_CFLAGS ?= -O2 -g -target bpf
 
-all: $(OBJS)
+all: $(SKELETONS)
 
 .PHONY: clean
 
 clean:
-	rm -f $(OBJS)
-	rm -f rss.bpf.skeleton.h
+	rm -f $(SKELETONS) $(SKELETONS:%.skeleton.h=%.o)
 
-$(OBJS):  %.o:%.c
+%.o: %.c
 	$(CLANG) $(INC_FLAGS) \
                 -D__KERNEL__ -D__ASM_SYSREG_H \
                 -I../include $(LINUXINCLUDE) \
                 $(EXTRA_CFLAGS) -c $< -o $@
 	$(LLVM_STRIP) -g $@
-	bpftool gen skeleton rss.bpf.o > rss.bpf.skeleton.h
-	cp rss.bpf.skeleton.h ../../ebpf/
+
+%.skeleton.h: %.o
+	bpftool gen skeleton $< > $@
+	cp $@ ../../ebpf/