[pxe] Fill in UNDIROMID pointer in !PXE structure

IBM's iSCSI Firmware Initiator checks the UNDIROMID pointer in the
!PXE structure that gets created by the UNDI loader.  We didn't
previously fill this value in.

src/arch/i386/interface/pxe/pxe_call.c

@@ -347,6 +347,9 @@ __cdecl void pxe_loader_call ( struct i386_all_regs *ix86 ) {
 	/* Copy parameter block from caller */
 	copy_from_user ( &params, uparams, 0, sizeof ( params ) );
 
+	/* Fill in ROM segment address */
+	ppxe.UNDIROMID.segment = ix86->segs.ds;
+
 	/* Set default status in case child routine fails to do so */
 	params.Status = PXENV_STATUS_FAILURE;