init_in has wrong size

[hanwen]

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.