done a dozen of randconfig test. guess what? ALL failed...
these are resulting fixes
diff --git a/modutils/insmod.c b/modutils/insmod.c
index 3b71d1c..842ef09 100644
--- a/modutils/insmod.c
+++ b/modutils/insmod.c
@@ -63,6 +63,7 @@
 #include <sys/utsname.h>
 
 #if !ENABLE_FEATURE_2_4_MODULES && !ENABLE_FEATURE_2_6_MODULES
+#undef ENABLE_FEATURE_2_4_MODULES
 #define ENABLE_FEATURE_2_4_MODULES 1
 #endif