Adding dispatchers to kallsyms. It's displayed as
  bpf_dispatcher_<NAME>

where NAME is the name of dispatcher.
Signed-off-by: NJiri Olsa <jolsa@kernel.org>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200312195610.346362-12-jolsa@kernel.orgSigned-off-by: NAlexei Starovoitov <ast@kernel.org>