samba: Add support for libnss_win*.so* installation

The libnss_wins and libnss_winbind libraries are required in order to
add support for the wins and winbind sources to the Name Service Switch
(NSS), so make it possible to install them. This is useful in order to
resolve NetBIOS names or user and group information from a Windows NT
server.

These libraries are installed to /lib/ like the standard libnss_*
libraries from (E)GLIBC.

[Thomas: remove useless comments.]

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau.dev@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>