selftests/bpf: test_verifier verbose log overflows

selftests/bpf: test_verifier verbose log overflows

Tests:
 - 458/p ld_dw: xor semi-random 64-bit imms, test 5
 - 501/p scale: scale test 1
 - 502/p scale: scale test 2

fail in verbose mode due to bpf_vlog[] overflowing. These tests
generate large verifier logs that exceed the current buffer size,
causing them to fail to load.

Increase the size of the bpf_vlog[] buffer to accommodate larger
logs and prevent false failures during test runs with verbose output.

Signed-off-by: Gregory Bell <grbell@redhat.com>
Link: https://lore.kernel.org/r/e49267100f07f099a5877a3a5fc797b702bbaf0c.1747058195.git.grbell@redhat.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>