selftests/bpf: test_xdp_veth: Remove unecessarry check_ping()

selftests/bpf: test_xdp_veth: Remove unecessarry check_ping()

check_ping() directly returns a SYS_NOFAIL without any previous
treatment. It's called only once in the file and hardcodes the used
namespace and ip address.

Replace check_ping() with a direct call of SYS_NOFAIL in the test.

Signed-off-by: Bastien Curutchet (eBPF Foundation) <bastien.curutchet@bootlin.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://patch.msgid.link/20250131-redirect-multi-v4-3-970b33678512@bootlin.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>