lib/fs: fix issue when {name,open}_to_handle_at() is not implemented

lib/fs: fix issue when {name,open}_to_handle_at() is not implemented

With commit d5e6ee0dac64 the usage of functions name_to_handle_at() and
open_by_handle_at() are introduced. But these function are not available
e.g. in uclibc-ng < 1.0.35. To have a backward compatibility check for the
availability in the configure script and in case of absence do a direct
syscall.

Fixes: d5e6ee0dac64 ("ss: introduce cgroup2 cache and helper functions")
Cc: Dmitry Yakunin <zeil@yandex-team.ru>
Cc: Petr Vorel <petr.vorel@gmail.com>
Signed-off-by: Heiko Thiery <heiko.thiery@gmail.com>
Reviewed-by: Petr Vorel <petr.vorel@gmail.com>
Signed-off-by: David Ahern <dsahern@kernel.org>