Comment to aid init_ssl_ctx understanding.

lib/net_mosq.c

@@ -457,6 +457,9 @@ static int net__init_ssl_ctx(struct mosquitto *mosq)
 		}
 	}
 
+	/* Apply default SSL_CTX settings. This is only used if MOSQ_OPT_SSL_CTX
+	 * has not been set, or if both of MOSQ_OPT_SSL_CTX and
+	 * MOSQ_OPT_SSL_CTX_WITH_DEFAULTS are set. */
 	if(mosq->tls_cafile || mosq->tls_capath || mosq->tls_psk){
 		if(!mosq->ssl_ctx){
 #if OPENSSL_VERSION_NUMBER < 0x10100000L