wafsamba: use private extentions also for bundled public libraries

wafsamba: use private extentions also for bundled public libraries

Playing tricks with redefining libraries, which may also be installed in
the system with the same version, isn't really a good thing.
It may work in some cases, but there are so many things which may go
wrong. So if we build a library as private/bundled library we should
change the soname of the library.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14780

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>