core: specify an activation reason for active connections

Specify a reason when creating active connections. The reason will be
used in the next commit to tell whether slaves must be reconnected or
not if a master has autoconnect-slaves=yes.

src/nm-act-request.h

@@ -41,6 +41,7 @@ NMActRequest *nm_act_request_new          (NMSettingsConnection *settings_connec
                                            const char *specific_object,
                                            NMAuthSubject *subject,
                                            NMActivationType activation_type,
+                                           NMActivationReason activation_reason,
                                            NMDevice *device);
 
 NMSettingsConnection *nm_act_request_get_settings_connection (NMActRequest *req);