add -Wundef, fix uncovered bugs
diff --git a/networking/interface.c b/networking/interface.c
index 6c8e938..8bbde7d 100644
--- a/networking/interface.c
+++ b/networking/interface.c
@@ -738,7 +738,7 @@
 
 #include <net/if_arp.h>
 
-#if (__GLIBC__ >=2 && __GLIBC_MINOR >= 1) || defined(_NEWLIB_VERSION)
+#if (__GLIBC__ >=2 && __GLIBC_MINOR__ >= 1) || defined(_NEWLIB_VERSION)
 #include <net/ethernet.h>
 #else
 #include <linux/if_ether.h>