DEBUG: applet: instrument appctx_wakeup() to log the caller's location

DEBUG: applet: instrument appctx_wakeup() to log the caller's location

appctx_wakeup() relies on task_wakeup(), but since it calls it from a
function, the calling place is always appctx_wakeup() itself, which is
not very useful.

Let's turn it to a macro so that we can log the location of the caller
instead. As an example, the cli_io_handler() which used to be seen as
this:

  (gdb) p *appctx->t.debug.caller[0]
  $10 = {
    func = 0x9ffb78 <__func__.37996> "appctx_wakeup",
    file = 0x9b336a "include/haproxy/applet.h",
    line = 110,
    what = 1 '\001',
    arg8 = 0 '\000',
    arg32 = 0
  }

Now shows the more useful:

  (gdb) p *appctx->t.debug.caller[0]
  $6 = {
    func = 0x9ffe80 <__func__.38641> "sc_app_chk_snd_applet",
    file = 0xa00320 "src/stconn.c",
    line = 996,
    what = 6 '\006',
    arg8 = 0 '\000',
    arg32 = 0
  }