bpf: add destructive kfunc flag

Add KF_DESTRUCTIVE flag for destructive functions. Functions with this
flag set will require CAP_SYS_BOOT capabilities.

Signed-off-by: Artem Savkov <asavkov@redhat.com>
Link: https://lore.kernel.org/r/20220810065905.475418-2-asavkov@redhat.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>