catch erroneous no-op makefile

iptables-extension/Makefile

@@ -5,12 +5,15 @@ XTABLES		= $(shell test -e /usr/include/xtables.h && echo 1)
 IPTABLES	= $(shell test -e /usr/include/iptables.h && echo 1)
 IP6TABLES	= $(shell test -e /usr/include/ip6tables.h && echo 1)
 
+WORK=0
+
 .PHONY: all module clean
 
 all: module
 
 ifeq ($(XTABLES),1)
 
+WORK=1
 module: libxt_MEDIAPROXY.so
 
 libxt_MEDIAPROXY.so: libxt_MEDIAPROXY.c
@@ -19,9 +22,11 @@ libxt_MEDIAPROXY.so: libxt_MEDIAPROXY.c
 else
 
 ifeq ($(IPTABLES),1)
+WORK=1
 module: libipt_MEDIAPROXY.so
 endif
 ifeq ($(IP6TABLES),1)
+WORK=1
 module: libip6t_MEDIAPROXY.so
 endif
 
@@ -33,5 +38,10 @@ libip6t_MEDIAPROXY.so: libxt_MEDIAPROXY.c
 
 endif
 
+ifeq ($(WORK),0)
+module:
+	@echo No iptables dev packages installed!
+endif
+
 clean:
 	rm -f libxt_MEDIAPROXY.so libipt_MEDIAPROXY.so libip6t_MEDIAPROXY.so