init_in has wrong size

compare https://github.com/libfuse/libfuse/blob/master/include/fuse_kernel.h#L799
and https://github.com/uroni/fuseuring/blob/master/fuse_kernel.h#L635

my kernel sends 104 bytes on init,  not 56.  The check 

```
  if(init_in->header.len!=sizeof(InitInMsg))
```

should be relaxed a bit.

