Pick up the gPXE include files when building prototester.

src/util/Makefile

 	$(CC) $(CFLAGS) $(EXTRA_CFLAGS) -Wall -lpcap -o $@ $<
 
 prototester.o : prototester.c
-	$(CC) $(CFLAGS) $(EXTRA_CFLAGS) -Wall -o $@ -c $<
+	$(CC) $(CFLAGS) $(EXTRA_CFLAGS) -Wall -o $@ -c $< -idirafter ../include
 
 prototester : prototester.o $(BLIB)
 	$(CC) -o $@ $< -lc $(BLIB)