selftests/bpf: Use ifname instead of ifindex in XDP compliance test tool

Rely on interface name instead of interface index in error messages or
logs from XDP compliance test tool.

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/7dc5a8ff56c252b1a7ae29b059d0b2b1543c8b5d.1678382940.git.lorenzo@kernel.org