fuse passthrough: fix cache files closed by lru in passthrough model

[wswsmao]

In passthough model, close will be toke over by go-fuse, so file.Close is unnecessary

[wswsmao]

before：
cache file will be close and go-fuse ioctl will return bad descriptor
https://github.com/hanwen/go-fuse/blob/master/fuse/passthrough_linux.go#L27

after：
Registration successful，and we can find read passthrough log by ftrace：

 9)   9.637 us    |    } /* fuse_passthrough_read_iter [fuse] */
  9)   9.955 us    |  } /* fuse_file_read_iter [fuse] */
  9)               |  fuse_file_read_iter [fuse]() {
  9)               |    fuse_passthrough_read_iter [fuse]() {
  9)               |      backing_file_read_iter() {
  9)   0.150 us    |        override_creds();
  9)               |        vfs_iter_read() {
  9)               |          rw_verify_area() {
  9)               |            security_file_permission() {
  9)               |              selinux_file_permission() {
  9)               |                inode_security() {
  9)   0.164 us    |                  __cond_resched();
  9)   0.494 us    |                }
  9)   0.148 us    |                avc_policy_seqno();
  9)   1.080 us    |              }
  9)   0.144 us    |              bpf_lsm_file_permission();
  9)   1.699 us    |            }
  9)   2.014 us    |          }
  9)               |          do_iter_readv_writev() {
  9)               |            ext4_file_read_iter() {
  9)               |              generic_file_read_iter() {
  9)               |                filemap_read() {
  9)   0.151 us    |                  __cond_resched();
  9)               |                  filemap_get_pages() {
  9)               |                    filemap_get_read_batch() {
  9)   0.147 us    |                      __rcu_read_lock();
  9)   0.144 us    |                      __rcu_read_lock();
  9)   0.146 us    |                      __rcu_read_unlock();
  9)   0.146 us    |                      __rcu_read_unlock();
  9)   1.457 us    |                    }
  9)   1.756 us    |                  }
  9)   0.152 us    |                  folio_mark_accessed();
  9)               |                  touch_atime() {
  9)               |                    atime_needs_update() {
  9)   0.152 us    |                      make_vfsuid();
  9)   0.146 us    |                      make_vfsgid();
  9)   0.749 us    |                    }
  9)   1.039 us    |                  }
  9)   4.186 us    |                }
  9)   4.467 us    |              }
  9)   4.750 us    |            }
  9)   5.053 us    |          }
  9)   0.177 us    |          __fsnotify_parent();
  9)   7.849 us    |        }
  9)   0.146 us    |        revert_creds();
  9)               |        fuse_file_accessed [fuse]() {
  9)   0.145 us    |          fuse_invalidate_atime [fuse]();
  9)   0.429 us    |        }
  9)   9.322 us    |      }
  9)   9.739 us    |    }
  9) + 10.051 us   |  }

[ktock]

We shouldn't enable this for blobCache.

Rather than globally control this mode, can we pass the PassThrough flag to the cache as an option of *directoryCache.Get?