bpf: Move lnode list node to struct bpf_ksym

bpf: Move lnode list node to struct bpf_ksym

Adding lnode list node to 'struct bpf_ksym' object,
so the struct bpf_ksym itself can be chained and used
in other objects like bpf_trampoline and bpf_dispatcher.

Changing iterator to bpf_ksym in bpf_get_kallsym function.

The ksym->start is holding the prog->bpf_func value,
so it's ok to use it as value in bpf_get_kallsym.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20200312195610.346362-6-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>