[pxe] Display PXE_LOADER debug message after call to initialise()

At least one Dell system calls the UNDI loader entry point with the
BIOS console disabled.  The serial console is active only after a call
to initialise(), so move the debug message in undi_loader() so that it
can be displayed via the serial console.

src/interface/pxe/pxe_loader.c

  */
 PXENV_EXIT_t undi_loader ( struct s_UNDI_LOADER *undi_loader ) {
 
-	DBG ( "[PXENV_UNDI_LOADER to CS %04x DS %04x]",
-	      undi_loader->UNDI_CS, undi_loader->UNDI_DS );
-
 	/* Perform one-time initialisation (e.g. heap) */
 	initialise();
 
+	DBG ( "[PXENV_UNDI_LOADER to CS %04x DS %04x]",
+	      undi_loader->UNDI_CS, undi_loader->UNDI_DS );
+
 	/* Set up PXE data structures */
 	pxe_init_structures();