nss: Finish renaming of HAVE_BSD_NSS macro

nss: Finish renaming of HAVE_BSD_NSS macro

When switching to meson, some of HAVE_* macros were renamed to
WITH_ because they did not reflect whether the build platform has
or doesn't have something, but whether we are building with some
functionality turned on or off. This is the case with
HAVE_BSD_NSS macro too. As a result, the NSS plugin built on BSD
did not expose nss_module_register() function which made the
plugin unusable:

https://www.redhat.com/archives/libvir-list/2020-September/msg00000.html

Fixes: c74268705557a6781788ba011492c15df2e3df11
Reported-by: Roman Bogorodskiy <bogorodskiy@gmail.com>
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Roman Bogorodskiy <bogorodskiy@gmail.com>
Reviewed-by: Jiri Denemark <jdenemar@redhat.com>