bpf/bpftool: Add unprivileged_bpf_disabled check against value of 2

bpf/bpftool: Add unprivileged_bpf_disabled check against value of 2

In [1], we added a kconfig knob that can set
/proc/sys/kernel/unprivileged_bpf_disabled to 2

We now check against this value in bpftool feature probe

[1] https://lore.kernel.org/bpf/74ec548079189e4e4dffaeb42b8987bb3c852eee.1620765074[email protected]

Signed-off-by: Milan Landaverde <[email protected]>
Signed-off-by: Alexei Starovoitov <[email protected]>
Acked-by: Quentin Monnet <[email protected]>
Acked-by: KP Singh <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]