delete_pipe uses DN_NR_HASH_MAX(16) instead of DN_PIPE_NR_MAX(65536): pipes 17-65536 undeletable — same as v1

Summary

delete_pipe(:1645) validates pipe_nr>DN_NR_HASH_MAX(16) not DN_PIPE_NR_MAX(65536). config_pipe accepts 1..65536. Copy/paste of hash bucket count instead of pipe space. Same bug as DF-0373 (v1). Resource leak: pipes 17-65536 only removable via FLUSH.