server supports it
for this, need NT CREATE AND X a directory in smbfs_open(), so that
we get the FID handle used for DIRECTORY CHANGE NOTIFY SMB
this could eventually be used to 'watch' even regular files, by
watching its parent directory and lookup/VN_KNOTE() when we get
REMOVED/RENAMED/MODIFIED action
also reorganize the kqueue code somewhat to use simplify locking
and knote detach
this is basically copy of what nfs_kq.c does - a thread periodically
polls server checking if any of the wateched files changed
eventually this should be changed to take advantage of SMB Directory
Change Notify
