thorium: use tracepoint message:transport_send and message:transport_receive

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
thorium: fix tracepoint message:transport_send

thorium_actor_profiler_profile communication_time= 12521586 ns (roundtrip latency)
Message Action 0x7724 Count 41 SourceActor 1000079 DestinationActor 1001601
thorium_message_print_tracepoints
message:actor_send 1122250451443661 ns
message:worker_send 1122250451443738 ns (+ 77 ns)
message:node_send 1122250451445005 ns (+ 1267 ns)
message:transport_send 1122250451445686 ns (+ 681 ns)
message:transport_receive - ns
message:node_receive 1122250455903822 ns (+ 4458136 ns)
message:worker_receive 1122250455904718 ns (+ 896 ns)
message:actor_receive 1122250455905890 ns (+ 1172 ns)

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
documentation: add documentation for tracepoints

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>