MINOR: tools: decode execution context TH_EX_CTX_INITCALL

MINOR: tools: decode execution context TH_EX_CTX_INITCALL

When the execution context is set to TH_EX_CTX_INITCALL, the pointer
points to a valid initcall, and the decoder will show "kw registered
at %s:%d" with file and line number of the initcall declaration. It's
up to the caller to make the initcall pointer point to the one that was
set during the initcall. The purpose here is to be able to preserve and
pass that knowledge of an initcall down the chain so that future calls
to functions registered via the initcall are still assigned to it.