nsswitch/nsstest.c: Avoid nss function conflicts with glibc nss.h

nsswitch/nsstest.c: Avoid nss function conflicts with glibc nss.h

glibc 2.32 will define these varibles [1] which results in conflicts
with these static function names, therefore prefix these function names
with samba_ to avoid it

[1] https://sourceware.org/git/?p=glibc.git;a=commit;h=499a92df8b9fc64a054cf3b7f728f8967fc1da7d

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Reviewed-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Noel Power <npower@samba.org>
Autobuild-User(master): Noel Power <npower@samba.org>
Autobuild-Date(master): Tue Jul 28 10:52:00 UTC 2020 on sn-devel-184

(cherry picked from commit 6e496aa3635557b59792e469f7c7f8eccd822322)