bpf: Emit global subprog name in verifier logs

We have the name, instead of emitting just func#N to identify global
subprog, augment verifier log messages with actual function name to make
it more user-friendly.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20231124035937.403208-2-andrii@kernel.org