fuse: don't access transport layer structs directly from the fs layer

fuse: don't access transport layer structs directly from the fs layer

Add helpers (get and set functions mainly) that cleanly separate the
layers.

Remove #include "fuse_dev_i.h" from:

 - inode.c
 - file.c
 - control.c

Remove #include "dev_uring_i.h" from inode.c.

[Li Wang: drop redundant initializer in process_init_limits()]

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>