proto_tls: disable async by default

According to ticket #2724, async tls might lead to unexpected behavior.
We are disabling it by default until we figure out what is going on and
fix the core problem.

modules/proto_tls/doc/proto_tls_admin.xml

@@ -509,7 +509,7 @@ param("proto_tls", "tls_send_timeout", 200) # number of milliseconds
 			operations like connect and write.
 		</para>
 		<para><emphasis>
-			Default value is 1 (enabled).
+			Default value is 0 (disabled).
 		</emphasis></para>
 		<example>
 			<title>Set <varname>tls_async</varname> variable</title>

modules/proto_tls/proto_tls.c

@@ -89,7 +89,7 @@ struct tls_mgm_binds tls_mgm_api;
 static int tls_port_no = SIPS_PORT;
 
 /* 1 if tls connect & write should be async */
-static int tls_async = 1;
+static int tls_async = 0;
 
 /* Number of milliseconds that a worker will block waiting for a local
  * connect - if connect op exceeds this, it will get passed to tls main*/