selftests/bpf: Add tests for BPF_NEG range tracking logic

selftests/bpf: Add tests for BPF_NEG range tracking logic

BPF_REG now has range tracking logic. Add selftests for BPF_NEG.
Specifically, return value of LSM hook lsm.s/socket_connect is used to
show that the verifer tracks BPF_NEG(1) falls in the [-4095, 0] range;
while BPF_NEG(100000) does not fall in that range.

Signed-off-by: Song Liu <song@kernel.org>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20250625164025.3310203-3-song@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>