dsm: don't use netbios struct members directly

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
contrib: fix libdsm and libtasn1 rules

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
contrib: update libdsm to 0.0.3

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
Require libdsm >= 0.0.3

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
dsm/sd: discover in a separate thread

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>