split validate channel code in function ngx_http_push_stream_validate_channels to be reusable

include/ngx_http_push_stream_module_subscriber.h

@@ -33,7 +33,8 @@ typedef struct {
 } ngx_http_push_stream_requested_channel_t;
 
 static ngx_int_t    ngx_http_push_stream_subscriber_handler(ngx_http_request_t *r);
-ngx_http_push_stream_requested_channel_t * ngx_http_push_stream_parse_channels_ids_from_path(ngx_http_request_t *r, ngx_pool_t *pool);
+ngx_http_push_stream_requested_channel_t *ngx_http_push_stream_parse_channels_ids_from_path(ngx_http_request_t *r, ngx_pool_t *pool);
+static ngx_int_t    ngx_http_push_stream_validate_channels(ngx_http_request_t *r, ngx_http_push_stream_requested_channel_t *channels_ids, ngx_int_t *status_code, ngx_str_t **explain_error_message);
 
 static void         ngx_http_push_stream_subscriber_cleanup(ngx_http_push_stream_subscriber_cleanup_t *data);