iPXE is already capable of loading EFI drivers on demand (via
e.g. "chain UsbMassStorageDxe.efi") but there is currently no way to
trigger connection of the driver to any preexisting handles.
Add an explicit call to (re)connect all drivers after successfully
loading an image with a code type that indicates a boot services
driver.
Signed-off-by: Michael Brown <mcb30@ipxe.org>