Garbage collect NWFS and NCP bits which are now completely disconnected
from the tree since few months.

This patch is not targeted for MFC.
- Initialize variable in smbfs_rename() to silent compiler warning
- Fix smbfs_mkdir() return value (in case of error).

Reported by:	pho
smbfs_lookup() in the DOTDOT case operates on dvp->n_parent without
proper locking. This doesn't prevent in any case reclaim of the vnode.
Avoid this not going over-the-wire in this case and relying on subsequent
smbfs_getattr() call to restore consistency.
While I'm here, change a couple of SMBVDEBUG() in MPASS().
sbmfs_smb_lookup() doesn't and shouldn't know about '.' and '..'

Reported by:	pho's stress2 suite