utils.h: add OSMO_STRINGIFY and OSMO_VALUE_STRING macros

OSMO_STRINGIFY particularly allows putting port numbers from a #define into VTY
doc strings, like:

  #define FOO_PORT 2342
  DEFUN(...,
        "Foo UDP port (default: " OSMO_STRINGIFY(FOO_PORT) ")\n")

OSMO_VALUE_STRING creates value_string items with the string being exactly the
enum value's name. Replaces a similar macro def in fsm.c

Change-Id: I857af45ae602bb9a647ba26cf8b0d1b23403b54c
2 files changed