Don't use unreliable functions for function names

[labbott]

In the kernel, functions found on the stack may be unreliable and marked with a "?" before the name. These functions should not be used for determining the stacktrace. These functions are still being used e.g.

https://retrace.fedoraproject.org/faf/problems/bthash/?bth=1c41bc0506d4330bf460b1ad8fb4f9a65c49f484 has __acpi_map_table as the function but that function is marked as unreliable. Unreliable functions should not be used anywhere.