Fix -fno-common build failure.

--- ssl.h.org	Sat Jan 30 08:09:44 2021
+++ ssl.h	Sat Jan 30 08:09:56 2021
@@ -25,7 +25,7 @@
 
 #include "types.h"
 
-_s32 ssl_cli_tap, ssl_srv_tap;
+extern _s32 ssl_cli_tap, ssl_srv_tap;
 
 void ssl_setup(void);