scripts: add bpf/send_msg.bt

This script tracks spdk_thread_send_msg and
spdk_for_each_channel calls.  It also uses usym
to get the name of the function pointer passed to
these calls.

Signed-off-by: Jim Harris <james.r.harris@intel.com>
Change-Id: Ia0cf5b50538bd26a3e15e35cbab765fe3c327c73
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/7711


Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Reviewed-by: Changpeng Liu <changpeng.liu@intel.com>
Reviewed-by: Konrad Sztyber <konrad.sztyber@intel.com>