bpf: Move ksym_tnode to bpf_ksym

bpf: Move ksym_tnode to bpf_ksym

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

We need bpf_ksym object to be linked both in bpf_kallsyms
via lnode for /proc/kallsyms and in bpf_tree via tnode for
bpf address lookup functions like __bpf_address_lookup or
bpf_prog_kallsyms_find.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200312195610.346362-7-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>