selftests/bpf: Update xdp_redirect_map prog sections for libbpf

selftests/bpf: Update xdp_redirect_map prog sections for libbpf

xdp_redirect_map.c is a bpf program used by test_xdp_veth.sh, which is not
handled by the generic test runner (test_progs). To allow converting this
test to test_progs, the corresponding program must be updated to allow
handling it through skeletons generated by bpftool and libbpf.

Update programs section names to allow to manipulate those with libbpf.

Signed-off-by: Alexis Lothoré (eBPF Foundation) <alexis.lothore@bootlin.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://lore.kernel.org/bpf/20240721-convert_test_xdp_veth-v4-1-23bdba21b2f9@bootlin.com
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>