spa: make a new FREEWHEEL clock flag

When freewheeling, the clock is going faster than real time.
When freewheeling, skip samples in alsa sink/source.

src/pipewire/impl-node.c

@@ -864,6 +864,7 @@ static void check_properties(struct pw_impl_node *node)
 	if (strcmp(str, node->group) != 0) {
 		pw_log_info(NAME" %p: group '%s'->'%s'", node, node->group, str);
 		snprintf(node->group, sizeof(node->group), "%s", str);
+		node->freewheel = strcmp(node->group, "pipewire.freewheel") == 0;
 		recalc_reason = "group changed";
 	}
 

src/pipewire/private.h

@@ -636,6 +636,7 @@ struct pw_impl_node {
 	unsigned int visited:1;		/**< for sorting */
 	unsigned int want_driver:1;	/**< this node wants to be assigned to a driver */
 	unsigned int passive:1;		/**< driver graph only has passive links */
+	unsigned int freewheel:1;	/**< if this is the freewheel driver */
 
 	uint32_t port_user_data_size;	/**< extra size for port user data */