samples/bpf: Get rid of bpf_prog_load_xattr() use

Remove all the remaining uses of deprecated bpf_prog_load_xattr() API.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/bpf/20220202225916.3313522-7-andrii@kernel.org