Trash bug fixed.

We were setting va_dirlinkcount equal to vap->va_nlink. However,
va_dirlinkcount is actually supposed to be the count of directory
hard links. When a file system does not support directory hard
links, this value must be set to 1 or not set at all.

In the case of ctldir, va_dirlinkcount was set to 3. Now we set it
to 1 there, as well.

MacZFS 74 also would set 1 for va_dirlinkcount in dirattrpack,
although it is not immediately obvious because it is referred to
indirectly, as follows:

if (ATTR_DIR_LINKCOUNT & dirattr) {
	*((u_int32_t *)attrbufptr) = 1;  /* no dir hard links */
	attrbufptr = ((u_int32_t *)attrbufptr) + 1;
}

Thanks to Alex Blewitt and Björn Kahl for pointing to
https://github.com/alblue/mac-zfs/commit/613276b9c2e874eecbee8223d1c957a58f7ee779
where a similar issue was corrected in MacZFS 74.