s3:libsmb: Revert SMB Py bindings name back to libsmb_samba_internal

s3:libsmb: Revert SMB Py bindings name back to libsmb_samba_internal

In order to make it clear that the APIs in these Python bindings are
unstable and should not be used by external consumers, this patch
changes the name of the Python bindings back to libsmb_samba_internal.

To make the Python code that uses these bindings (i.e. samba-tool, etc)
look a little cleaner, we can just change the module name as we import
it, e.g.

  from samba.samba3 import libsmb_samba_internal as libsmb

Signed-off-by: Tim Beale <timbeale@catalyst.net.nz>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Autobuild-User(master): Stefan Metzmacher <metze@samba.org>
Autobuild-Date(master): Wed Jan  9 14:30:31 CET 2019 on sn-devel-144