IPMARK: import 20080304 code base

With truly minimal changes to make it compile.

extensions/Kbuild

@@ -8,6 +8,7 @@ obj-m                += compat_xtables.o
 obj-${build_CHAOS}   += xt_CHAOS.o
 obj-${build_DELUDE}  += xt_DELUDE.o
 obj-${build_ECHO}    += xt_ECHO.o
+obj-${build_IPMARK}   += xt_IPMARK.o
 obj-${build_LOGMARK} += xt_LOGMARK.o
 obj-${build_TARPIT}  += xt_TARPIT.o
 obj-${build_TEE}     += xt_TEE.o