Using plain shared memory for configuration pass.

There is no restrictions on configration size and using segmented shared memory
only doubles memory usage because to parse configration on router side,
it needs to be 'plain' e. g. located in single continous memory buffer.

src/nxt_port_memory.h

@@ -71,5 +71,6 @@ typedef enum nxt_port_method_e nxt_port_method_t;
 nxt_port_method_t
 nxt_port_mmap_get_method(nxt_task_t *task, nxt_port_t *port, nxt_buf_t *b);
 
+nxt_int_t nxt_shm_open(nxt_task_t *task, size_t size);
 
 #endif /* _NXT_PORT_MEMORY_H_INCLUDED_ */