libethernet: add Makefile

Makefile

+CC = gcc
+CFLAGS = -O2 -Wall -g
+
+objs_lib = ethernet.o
+
+ifeq ($(PLATFORM),BROADCOM)
+objs_lib += bcm.o
+else ifeq ($(PLATFORM),MEDIATEK)
+objs_lib += ethsw.o
+XXFLAGS += -Wl,-whole-archive -lsw -Wl,-no-whole-archive
+endif
+
+all: libethernet.so
+
+%.o: %.c
+	$(CC) $(CFLAGS) -fPIC -c -o $@ $<
+
+libethernet.so: $(objs_lib)
+	$(CC) $(CFLAGS) $(EXTRA_CFLAGS) $(LDFLAGS) -shared -o $@ $^ $(XXFLAGS)
+
+clean:
+	rm -f *.o *.so