MINOR: ssl: add global statement tune.ssl.force-private-cache.

Boolean: used to force a private ssl session cache for each process in
case of nbproc > 1.
diff --git a/include/types/global.h b/include/types/global.h
index 241afe9..cf61271 100644
--- a/include/types/global.h
+++ b/include/types/global.h
@@ -129,6 +129,7 @@
 		int cookie_len;    /* max length of cookie captures */
 #ifdef USE_OPENSSL
 		int sslcachesize;  /* SSL cache size in session, defaults to 20000 */
+		int sslprivatecache; /* Force to use a private session cache even if nbproc > 1 */
 		unsigned int ssllifetime;   /* SSL session lifetime in seconds */
 		unsigned int ssl_max_record; /* SSL max record size */
 #endif